Sue, I really feel for you. Something similar happened to my daughter. Her now ex took the children all bar the youngest and was so hostile it was unbelievable. The courts gave him custody despite him admitting he was on the sick because of mental problems. Can you believe it!!! The kids were brow beaten into fear of him and they wouldn't complain to Social Services. It wrenched our hearts out but the good news is that after 3 years, two of the children returned to Mum on their own accord and the eldest has now made a home for himself. It makes me wonder if the gov't demands a quota of children being placed with their father to prove some sort of 'equality' thing. Men can make good homes but some are so obviously not suitable I can't understand at all the logic of some court decisions.
Try and be strong for your daughter's and grandkids sakes. I know its hard but have hope that all will come well in the end.
Carolyn D