If the girls used to sleep in your room and now they are not this could be the issue for them, because they may be feeling a bit ousted( not sure if this is the proper word or spelling) from their routine. You may try to let them have your bedroom at night so they feel they have the same attetion at night, and he can wander the rest of the house and not feel threatend. The best thing to do is to make sure you are offering the same attention they used to get, and that way they do not feel that the intruding cat is really that big of a change for them.
I just added a third, very slightly older male to my two girls(mine are all under a year old,but very territorial), and they had some issues with him too, but I think theyare all working it out. We still have a hiss and smack now and then but I think that is normal. I have a water bottle out in case of a bad one, then the one starting the fight will get the water. It has not seemed to damage them meatally at all. Sometimes Lizzy has been sprayed when she has attacked Chloe, and now they just play really rough. Sometimes Chloe has been sprayed when she has attacked Connor, and she stilll loves me as much as before and keeps to her routine with me. Connor has been sprayed even trying to attack Chloe, but it does not work too much with him, because he happens to like water, but it did stop him the first time. I have not had to use it much, and now all I have to do is tell them to be nice and they stop fighting. I still keep the bottle handy just in case, but I think that it does help sometimes to interveen, and it teaches them that fighting will get them something they do not like, but it does not harm them.
I would not give up just yet, I feel there is always hope! Cats do not like chages in their routine, but senior cats are harder to get adjusted then younger ones I think.