Help! My Cat is having issues with my Teenage Sons

Hi wonderful TCS members.  I have been on this site quite a lot and have posted a few times and always have been met with so much helpful and nice advice that I find I again need your suggestions.  Sorry for long post, I will try and give all the info I can.

My cat Abra Rose is a desexed female who is 5 years old.  Abra has been living with us since January 2016. I got her from a young lady (23 years old) that was moving overseas and could not take her with her.  The young lady lived with her Mum, Dad, teenage brother, 2 x dogs and my cat.  These were the only owners that Abra knew and she had been with them since she was a kitten.

Abra is a very shy nervous cat and is frightened of everything (or so it seems).  Thanks to this site I have managed to get Abra to come more and more out of her shell and she no longer hides 24x7 and is actually now spends time up high (instead of under the bed in the cupboard etc).  Abra is scared when people visit but is slowly getting better.  I give her a treat if she stays in sight when people are over and this has helped a little. 

Abra currently lives with my self and my husband for the most part and every second weekend and school holidays my two teenage sons (17 years and 14 years) stay over.  This is where my problem is.  We have a small three bedroom house with an open plan lounge kitchen and study, bathroom and the 3 x beds. 

When my sons are not at home, Abra spends the majority of her time in either of their rooms mainly my eldest sons as they are the furthest from the noise and activity of the house.  They both have desks under their windows so she likes to look out on the world from there and she has decided that she likes to sleep on their beds (I have put down a blanket on each bed for her, to alleviate cat hair).  At night, Abra is locked out of our bedroom so normally will sleep in their room.  When they are at home, she will sleep in the study or lounge.

When the boys arrive they usually spend the majority of their time in their rooms but they are also out in the living area which makes it a lot noisier place.  When they are in their rooms Abra will occasionally go in there but usually she just sniffs around and leaves. 

Abra hisses at the boys when they walk, talk or are anywhere near her and the whole time they are at home she seems upset and unsettled.

We have tried:

The boys feed her dinner, give her treats when she seems quite and happy and stays in the room they are in.  Play da-bird with her.  Do slow blinks with her.

Possible issues that it could be:  The boys have a dog at their Dad's house (so this could be an issue)? the family that I got Abra from told me that the younger teenage son did not like her (maybe he did something that she now associates with all boys)?  Abra thinks the boys bedrooms are her territory so doesn't like them being in there?

Is there anyway we can get Abra to be more settled when my sons are at home or is this just going to be the way it is?

Thanks for any suggestions and if you need any other information let me know.

It may just take time, but one thing you could try is having them leave an unwashed shirt or two in the rooms so she can used to their scents when they aren't there. If she starts to associate their smells as normal things around the house, she may be more accepting when they're there in person.

Thank you so much for replying @Ms. Freya  that is something I haven't tried but is a great idea.  The boys are over this weekend so I will keep a shirt each out of the washing for when they have gone (being teenage boys their clothes do have a strong scent after wearing).  My youngest isn't overly worried that Abra doesn't like him but my eldest is upset and really wants to become her friend.

I'm not sure where you are, but if Feliway is available you should try it.  Get one or two of the plug ins and give it a week or two.  The pheromones put off by the plug ins, along with worn shirts of your sons', may work in combination to calm her down.

Thanks for reading my long post.  Yes Feliway is available here, I will give it a go, I hadn't done so yet because my Husband doesn't like plug-in stuff due to fire risk and I kept thinking that it would just get better with time but it hasn't.  I will get this sorted today before they arrive this weekend.

Update:  Thanks @Ms. Freya and @LavishSqualor for your advice. 

I purchased two by Feliways plug-ins (wow very expensive $110.00 each).  I put one in my eldest sons room and one in the living area.  I haven't really noticed any change in Abra overall yet, she still seems scared, shy and skittish in general but I have read it can take a few weeks to kick in (it will be two weeks tomorrow).

I have left a dirty pj shirt in both boys bedrooms.  Usually when they leave my house on the Monday morning Abra is back in their bedrooms that same day but it took her until Friday to go in there.  She did what she does when they are present goes in sniffs the air and walks out, so I think Ms. Freya was onto something with the scent.  Once she was in their rooms I gave her the shirts to sniff and she sniffed them and then me but actually stayed put in the room which I feel is a good sign.

When the boys were at home she did hiss at my eldest one time when he was walking past in the lounge room but other then that she wasn't hissing every time he was near her (which could be a sign the Feliway is doing something).

The boys are back at my house for an extended period for the school holidays starting Friday so fingers crossed that we start to see some improvements. 

Thanks again for your advice. 

Fingers crossed for you!

It may take her some time to adapt, but hopefully she considers them normal parts of the household before too long.