Supprting my son wth advice

Hi folks .
My son is 24 years old with a child that's 6 years old .
He has been struggling most of his life with a learning disability.
started out with speech imparement along with his son who has the same thing.
As well as low self of steam and confidents
like lots of people decided to try out drugs with his baby's mother unfortunately
he has a addicting personality she doesn't .
unfortunately they ended up slitting up when there child was 1.5 years old
With in the past 5 years he has gotten the help to get clean and has been doing great .
There for the mother of the child would back off but now that the drugs is out of the way
she is slandering him over child support.
Yes I realize its not easy to raise a child on your own without support however because
we live across the street from his school he offer to have him stay here and take the child to school.
That was a huge NO so she sends him to her parents across town at 7:30 pm and her dad takes him to school.
My son has bent over backwards to help her in anyway possible and has given her money when he could. that still wasn't good enough the slandering and try to keep the child away from him continues
Finally I asked her kindly believe it or not to stop and pointed out what he has done for her and that
was a huge NO as well
Having my family fed up with all the hassles there end up being a text message dispute between her
and another member of the family. this had nothing to do with the child and his father but she still
desided to punish both.
Any ideas how this can be prevented its so unfair to the child that loves to be with his dad.
Been to court lots of times but of course she doesn't stay because her lawyer is there and my son can't legal aid because he lives at home and that's how she all ways gets her own way.
my son gives in so he have  his visits at least until she gets angry again