Hi Mary,
First off, thank you for fostering : )
1) Either soak their mom's food in water until soft or grind up the dry food in a coffee grinder and then add water. You can mix in some of mom's wet food or kitten milk replacement (if you have it). Since they are 4 weeks old, they can start spending a little time away from their mom (and her sweet boobies). Try separating them for an hour or two which will do two things: allow them to get hungry enough to try the mush and give them time away from their not-so socialized mom.
2) It can be challenging and time consuming to socialize a fearful adult cat. I'd keep trying to gain her trust (I'm sure someone here can point you toward some good resources). If your time is limited, I would focus my energy on the kittens. They will learn to fear people from their mom BUT, the great news is that their temperaments are very flexible at this age. They should be gently handled and played with by as many different people as you can manage (like, 100). This does not mean you should give up on Mom but you will, almost definitely, have more luck with the kittens.
Good luck!
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Diane Zahorodny
World Ready Pets
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