How can we protect our female cat who gets harassed all the time by at least 6 tomcats in our garden?

Our female cat is not spayed yet, she is going to be tomorrow. She has two female kittens too, they’re with her all the time (they’re going to be spayed as soon as they reach the minimum weight for the procedure). The mother sleeps and protects herself and the kittens in a small cave-like space in our large garden (it is a common space for multiple residences).

Lately, I have been observing at least 6 different tomcats waiting just under her nose in the entrance of her little cave. She and her kittens are naturally extremely disturbed, they cannot even get out of the cave unless I am around.

I am going to take them to the vet tomorrow for spaying (mother) and a general check. But after the mother recovers I don’t know how I can put them back in the garden again. I already gave multiple ads to find home(s) to them. There has unfortunately been no return, and I have to move to another country two months later.

Do you have any suggestions for us?