They are adorable! And they are certainly old enough to eat some kitten dry and canned food. (probably 8-10 weeks old)

It is also EXTREMELY normal for your cats to not be fond of the new ones. You'd be best off to keep the babies in a room by themselves. Not only will you not have to worry about introductions (yet) but they will be close to their litter box. (and keep the adults out of the kitten food.)

If you plan to keep them, you can work on the introductions later.

Have fun, They look like a bundle of energy!