Good luck with them. Either try to get a bigger tank and put a divider in, or another smaller tank. Craigslist is the best
i learned putting a want ad actually works better than expected.
A lot of the time, when you first get bettas *maybe fish in general?* they won't eat for a while, mine seemed to be 2 weeks! the main problem is they are stressed, getting situated, getting used to the new water and such. don't worry about them not eating right now, they will when they get hungry. they are just stressed.
i also had to learn with one of my smallest that he won't eat if i am watching him. i have to leave the room for him to venture out far enough to eat * i got to see him eat for the first time yesterday! yay*
And once they get set up they are fairly inexpensive. Do you have a filter? if not i suggest weekly 20%-30%, depending on how bad it is, weekly or smaller amounts twice a week.
Don't worry they will adapt! just give them time.
and lots of good luck! pics?