Foster kittens only suckling wet food need help

My 4w kittens were taken from their mom and placed into my care and I am so worried because they are not gaining weight. My shelter provided me wet and dry food but they only suck at the wet food, ingesting very little. I give them one tablespoon four times a day. My issue is that while they are learning to bite and chew, I have no other way to get them any calories. If they were bottle fed, I’d still supplement formula. If they had their mom she would still take care of them.

What can I do to get more food into them while they figure it out? They do chew toys and bite each other and they do have their teeth, but the chew mechanics are just not there with the wet food. ‘Force feeding’ them by opening their mouths only stresses them out. Please help I am so worried!