MY CAT

How old is a kitten when she first hits her heat?

It depends, but some start puberty and going into heat as early as 4 or 5 months. 

OK.. awesome.. my cat is 5 months n I haven't gotten her, nor her mom nor pops fixed yet.. I believe her mom may be pregnant again, how would 5 month baby treat them?

A 5 month old is still a kitten, though in puberty.  It would treat them fine.  May be a little rough on them so you would need to keep an eye on her/him.  You need to get her spayed.... Pops will be trying to mate with daughter and you'll have inbred kittens.  Dad and daughter are not a great combination.  They all need to be asap. 

I got our momma kitty from a breeder who had not realized she had gone into heat at 5 months old.  Apparently, her male cat was pretty quick to take advantage!