The older female is and as soon as I can I'm getting the younger one spayed. Could that have something to do with it?

Altered?

I have 2 females one is 2 the other is 10 months old. It not that they fight, it just they co-exist, its like if one cat is next to you the other stays across the room, no fights just avoided hissing. It hasn't been short term either this has been go...