9 week old male brothers. Fatcat is a stray we adopted 3 years ago - vet reckons she's about 6. The kittens were adopted after our previous female was hit by a car. She got on ok with other cat but never exactly friends... But she spits and makes that weird moaning tummy growl whenever she sees them. I feel sorry for her as it's as if she feels driven out. What can we do? Will having the kittens neutered help?