You shouldn't free range your birds in a neighborhood because someone might take them, thinking they're stray. At the very least, you need a coop.
Have you considered whether you can afford chickens at this point? What happens if one gets injured or sick? Will your foster parents pay for its care?
Ask them what they mean by "help you with the feed". Will they pay for all of it, or just some of it?
If you're planning to get animals to take care of, you need to figure out how you'll afford food and basic medical care for them.