fft100 - You're in a really difficult position regarding what to do with these little wild kittens (and their mum). One thing I would say is that I very much doubt that you'll be able to find someone to humanely 'dispose' of them. Most vets won't do it - even if the animal is in serious pain.
When we lived in Petchaburi we ended up with two semi-wild female dogs giving birth (within a week of each other) to a total of 13 pups. They were born in flower beds near our kitchen, so I couldn't ignore them. We fed them good food, so they were all healthy and cute. A local woman in the village took them away (two or three at a time) and sold them from her vegetable stall

. I have no idea where they went, or what happened to them after they were sold, but it was a solution to the problem.
If you could make sure that they get enough food so that they look cute and healthy, put pretty little collars on them, and then find someone to sell them on, it could be an option.
One more thing: I was told by a vet that the best milk to feed kittens or puppies is powdered baby milk. It builds them up and has all the vitamins a young animal needs. I know you don't want to keep them, but the fatter and cuter they are the more likely that someone will want to take them off your hands.
Good luck...I hope this story has a happy ending.
VS