A lot of behavioral things went on the past month

The main reason that I have one of my cats with me and the other two are with my mom is because I dont have room for two cats. All three of my cats are fixed and in good health. There is a 14 month old female that has the mentality of a 8 month old. A 5 year old male who adores the 14 month old. And a 15 year old that sleeps, hogs the water, and stares out of windows. They had gotten along for 7 months with no issues, the 5 year old and 15 year old had been living together happily for 2 years.. almost 3 years now.

About five weeks ago my mom called me, all three cats had been living happily at our home, but the two younger ones woke her up trying to be rid of the 15 year old through aggressive behaviors. For two weeks the behavior got worsened as my mom tried to stop them from literally hunting the 15 year old. The 14 month old kitten began urinating on carpets and rugs. and the 15 year old had to live in a xxl dog crate with no one home to ensure her safety.

The 15 year old became stressed and over groomed. The logical move was for me to take the 15 year old back to college with me after my visit home. So I did and she's doing great! Before I brought her up here I had full agreement from all of my roomates. All of the human and dog roomates. There's one other cat here, and he is notoriously known throughout my roomates circle of friends, for urinating on other cats.

Does anyone know:
1. what could cause the younger cats to suddenly want to take the life of the 15 year old?
2. is it possible the overgrooming and stress from being in a crate is related to the cats past of living in a hampster cage (prior to my ownership)?
3. what would make my roomates cat pee ON other cats? I understand spraying and urinating to mark territory.. does this mean he wants to own every cat in the vicinity?

thanks in advanced!

The 15 yr old was at the vet last weekend and her liver functions are normal, her blood counts good, and the only problem that's been existing is a slight heart murmur other than the over grooming which they gave her a cortisone shot and a e-collar and antibiotics. I'm glad to hear its probably related to the stress of what was going on, I don't want her to go through it ever again so I know what to avoid now.

The 14 month old still stumbles and falls off of things like a clumsy kitten.. some weird neurological thing with her brain? The vet explained it as an infection when she was feral that her mother had and passed on to her that caused her brain to swell and some sort of damage was caused?

As for my roomates cat being neutered.. I'm not entirely sure he's even a he. Her vets reply after she got him fixed (three years ago) she took him in to "get his stitches out" which is what the vet told her over the phone.. then they said "oh he doesnt have stitches, we glued him". Her cat has a lot of mental issues.. a college dude stepped on his paw by accident and broke it when he was a kitten, and a week later another very tall college dude accidentally held kitty up close enough to bump into a fan that was on.. I have been here for 2 months, seen her cat 6 times? But apparently if he finds out China Doll is here, he'll pee on her.

No actually now that you mention it, they have never checked her thyroid before.. she has even had seizures in the past (treatment was very worrisome with her heart murmur) and a virus/flu sort of acting illness that they never diagnosed but said she was "healthy and it should pass if we treat the symptoms". She has been tested for the feline leukemia/hiv equivalent diseases. It was our first test we even ran on her because it would have determined if we spoiled her for her "two weeks" left of life or if we euth'd her (we had Jason at home and didn't want to get him sick).

And we can call her China Doll... I may call her Noel out of habit it's the name we gave her when we got her (Nov. 22, 2008).. her name when we got her at 13 years old was "Creature" (on a tag with the phone number to a foreclosed home that was sitting at the bottom of the cage).
Funnyish story about her name being Noel- she had seizures last year, December 24th and 25th due to (no surprise here) and infection causing the brain to swell < I think there are many cats with this issue in my old neighborhood due to the high levels of feral cats running around. She hasn't had one seizure since then.. Our emergency vet was like "is that a joke or is that really her name?"

I'm having to switch vets anyways since I moved her up here so she'll be getting another checkup soon. Mom has a cat veranda, so they are indoor but they do have access to the outside and other cats could come in contact with them I suppose.. China Doll was an escape artist, she isn't so much now but she would bolt any chance possible..

I hope she doesnt get seizures again.. That was awful to experience.. I read somewhere that animals may start seizing due to hypo/hyper glycemia or something? I am going to have her bloodwork done again once she's settled in here (she's been here with me for a little over a week). I'll make sure they check her sugar levels and her thyroid. She does drink a ton of water, but right now we've put her on hard food (I want to raw feed her but I dont think her immune system can handle it).