Help My Cats Won't Meow

I have two cats a Manx(nubbin) and a main coon(serena). recently my mom braught anew cat into the house. both cats were upset by this and would find the kittie and hiss at her. after two weeks they have started to get along with her but both cats ecspecailly Nubbin have stopped meowing.
ususally when nubbin sees me me she meows and and comes to me and she'll follow m around... well she still follows me but her meow and serena's is quiet almost no sound coming out and it sounds raspy. does anyone have any idea what it might be? or what i can do for them.
-Kathleen

See this thread.

http://www.thecatsite.com/forums/showthread.php?t=62246

Since cats meow mostly just to talk to people, people can encourage their cats to meow by talking to them.