no heat, but looks and acts pregnant

Two weeks ago my family went on vacation but our cats stayed home, my mom and I have been worried about one of our male cats because he's not fixed and we have two female cats not fixed either. When we came back I had a suspision that the male's sister was pregnant, she is under a year but over 7 months, she has never gone into heat but her nipples have gone pink and she's showing sign's of wanting more affection, and her belly is getting bigger. Is it possible for a cat who has never gone into heat to get pregnant?

She might have gone into heat and had no one notice it, or may be having a false pregnancy.
   
The only way you can tell is to bring her to a vet and have her spayed ASAP.
   
There are far too many litters being euthanized at shelters in our community to allow more to be brought to term, and if it is a false pregnancy you have a decent risk of her getting a fatal infection. I'd take schedule an appt to have her spayed immediately and not take the risk.
   
(And please get your other cats fixed at the same time)