My mom started out hating snakes, partially because my dad had a nine foot burmese when she was pregnant with me, but she is okay being around my ball python and my california kingsnake. The best advice I have for helping them get over it is to not push the subject, if you bring it up and they clam up then drop it. I feel once they see you won't force the subject on them they may warm up to the idea. That being said everyone is different I know some people that no matter how much I try are absolutely terrified of snakes. I wish you luck on that aspect.

As far as pet store snakes are concerned I advise against buying ANY animal from the big pet chains, pet .co and petsmart mainly, I got my ball python from a specialty store and he is doing just fine. Hits rats like it's cool and has shed four times for me since I got him. The kingsnake is wild caught so can't give pointers on him... If you are going to buy a snake from a pet store like petsmart then I suggest you familiarize yourself with what a healthy snake looks and acts like. You can't be to careful with pet stores like that. I'm going to stop there before I rant about it.

Now for rats and snakes in the same house, that's fine go for it, just make sure you wash your hands VERY WELL in between the two. I always make sure to wash my hands after handling my ball python and the cal king and visa versa. I don't want to get bit by the cal king and I don't want to spread possible illness. As long as you don't do that you should be good, I also would consider different rooms for the two, but that's just me. Hope this helped, I'm no expert and there are people on this site who know WAY more than I do. I'm sure they'll chime in if they feel the need.