Update: Mother cat left her kittens.

I haven't seen mumma cat since 1 am last night when I tried to feed her. I thought she'd come back after some time. But, the kittens are not eating anything now. They don't make any noise when they are in the box and when I take them outside, they just visibly look for their mother. Food and water goes untouched. They honestly look distressed outside the box. Now, they can open their eyes fully. I'm not sure what to do with them now.

I tried looking for the cat on all the floors. I'll again look for her in the parking lot. As it's raining outside, I don't think she's gonna roam around anywhere which doesn't have sheds. Unless the cat was coming when I didn't check up on them, the kittens haven't consumed anything since 1am. Also, I haven't seen them pooping since I first saw them yesterday morning.

Also, Which products can I use to clean the kittens? That seems like the best way to convince my mum to take them inside the house.