Help! My Feral's Bully Behavior Chased Away My Other Cat

[ For some background information, my cats were all feral kittens (siblings) when I began feeding/spending time with them.  They experienced a fearful kittenhood around humans that scared/mistreated them. They are now 1 years old. They are mostly outdoor cats, but will soon be transitioning indoors when I move in 1 month. They are all neutered and spayed. ]

For three weeks, Osric has not returned home aside from 2 very brief stop-ins for food. Osric used to mostly stay in our yard, play in our yard, and was always on time for food. She'd always come when she was called. Her bonded partner, Sable, was attempting to mount her with increasing frequency in the weeks prior to her leaving. She would paw his face away and hiss. She no longer stayed in the yard, and preferred to stay on the driveway. Then, my family experienced a flea infestation. The cats could no longer come inside for 3 weeks until the infestation was fully treated and their medications switched for a better fit. Sable, who spent 6 hours a day indoors, was the most poorly affected. I'm not sure if the ban from indoors increased his mounting attempts. One day, Osric did not show up for breakfast, and she didn't show up at night during playtime. She continued not to show up til now. I spotted her twice in the yard during her time gone. She came when I called her over. I attempted to feed her, but quickly, Sable would appear and attempted to mount her. Her immediate reaction was to push him off and leave. 

I've been trying to curb Sable's behavior, but I don't know where to begin. One article I read mentions reaffirming his dominance to decrease his need to enforce top cat status through force. But he already has first pickings on their resources. He receives the most attention, because he's the most attached and readily available. He gets first feedings (because he's always around me), he gets the most massages (he's the most tactile), he gets the most play (always around to play), and he gets the cozy blankets (he chases his siblings away when he wants them).

One possible factor in Sable's escalation is that a neighborhood outdoor un-neutered tomcat has been beating my cats. 3-4 times a week, he comes by to stalk them, fight them, and mount them. He is bigger than they are. I've been chasing him away at every opportunity. Sable was mounted twice by him before I stopped him. I don't know if this cat as a home; he doesn't belong to my neighbors, but he acts like a fully socialized cat. I don't think he's a feral. Either way, I haven't been able to locate an owner to keep him away. I'm not sure if this is a factor in increasing Sable's mountings of Osric. Previously, he used to mount her from time to time, but she didn't seem to mind as much. They used to everything together, from sleeping, eating, and playing. Then again, they are no longer kittens, and perhaps this is when cat hierarchy begins really setting in. 

I'm not sure how to positively curb Sable's behavior and make the yard a safer place for Osric.  I've been so worried about her outside, where she's likely been hunting her own food (they are all mousers). She's extremely wary around other people, so I doubt she's approached other humans for food.  If anyone has any suggestions, that'd be terrific.

More information on their living situation in last year's thread here: http://www.thecatsite.com/t/306878/...-i-have-to-capture-them-for-spaying-neutering

*Thread is also cross-posted to "Cat Behavior." I'm not sure if this is the right category for semi-feral behaviors, and if it's not, I'll take this post down right away.

This is a very difficult situation.  I had a similar experience a few years ago.  It is very hard to curtail the behavior of these cats.  My poor little one (Shadow) was being chased away from his home.  It was crushing.  I was able to temporarily move his eating and sleeping area to our front porch.  The other cat (Marvin) would leave him alone there.  I worked with Shadow on play therapy to help boost his confidence.  This did help him.  Yet anytime he saw Marvin, he was so scared he would just run.  I had no idea what to do.  I cried way too many tears over this issue.  Marvin eventually found the front porch.  It was clear he did not want Shadow there.  Both cats were feral, neutered males.  Marvin had only been with us about 5 months when the troubles began.  I tried to find a new location to relocate Marvin.  I was not successful.  I decided my only solution was to move Marvin inside permanently.  He also had chased off one of my other feral cats during the winter. 

My solution was a drastic one, but it turned out to be a win win for all.  It took Marvin an entire year to acclimate and also get used to my resident indoor only cat.  It was tons of working introducing them, but after a year life settled down.  They are buddies now and Marvin is a sweet still scared kitty.  Shadow moved back onto his deck and this time with a bit more confidence.  The feral cats continued to arrive, but none have caused issues like Marvin.

I would suggest setting up a safe location for the female kitty.  Be sure that she knows that you will protect her.  Keep Sable away from her while she is there.  If possible bring one of them inside full time.

It is possible that the female has moved on.  She may be not only having issues with Sable, but also the tom cat.  She may have found another source for food or is hunting. 

I hope the best for all of the kitties.  The hardest part of caring for these sweet ones is the lack of control we have over them. 

The best solution would be to move Osric back indoors. You'll be transitioning them all back indoors when you move in a month, right? Right now, you want to do everything you can too keep them all together so that none of them run off before you move. 

I have a domesticated feral male, Harry, who is the alpha male in my house. Almost two years ago, I brought in a rescued outdoor cat, Sonny, who also wanted to be the alpha male. At first they fought all the time inside my home, though thankfully there was no territory marking and no wounding except for the occasional scratched nose on Sonny. Over time, they've learned to co-exist with only an occasional squabble. I brought in a female feral kitten 4 months ago, and she has bonded  closely with Harry, and now also Sonny, and it occurred to me the other day that now Harry and Sonny hardly fuss with each other at all. There is harmony in my house of 5 cats.

My experience has taught me that indoor cats learn to co-exist and work out there differences because they have too--there's no other choice, there's no chasing another cat off to another territory. They learn to share resources and space. Once you get all your cats indoors, there will be some initial chaos--but then they will work it out. Cats are social creatures and create their own hierarchy. The challenge for you now is to keep all of them safe and together until your move, so if you can begin to transition them indoors now, that would be ideal. I've found Frontline Plus to be the most effective for keeping fleas off cats for a month, and you can it on Ebay and Amazon in multi-packs for about a third of the cost of a vet's office or pet store. Once the cats are all indoor cats only, fleas will stop being a problem.

Good luck, and I hope everything works out for you and your kitties.

Thanks so much for the excellent advice! I won't be able to move Osric indoors 24/7 because of my current living situation, but I will set up a safe place for her in the shed. Hopefully she takes to it, since she's not comfortable in small confined spaces. I just have to remind myself that it'll be temporary. In the meantime, since she's left again, I'll also move Sable indoors for his max 6 hours to keep him away from her if/when she does return. 

@MsAimee  Thanks for the flea medication rec! Two of them are on Advantage II, and the touch-shy ones are on Program Green + Capstar. They were previously on Activyl. I'll try Frontline Plus next to discourage the fleas from developing an immunity to Advantage. I'm also relieved to hear that they'll likely be able to work out their differences in the same indoors household. I was worried it would be a warzone with Sable antagonizing and Osric running, and am so glad to hear that your kitties are living in happy harmony.

@ShadowsRescue  Thanks for sharing your story and solutions with Shadow and Marvin. I'm glad to hear that your drastic solution has worked out in the best way. It is hard caring for the sweet ones, trying to give them love and attention without setting off the top cat (who is also very affectionate, but can be an absolute bully to his siblings). Osric is gentlest and the second smallest of the litter. She and Sable used to protect each other. It pains me to think that she's been chased out of her home while former partner and protector has run of the place.