The OP started paying into her GC's college fund as soon as he was born AmberSpyglass. This is not something she started to try and bribe (her) way past boundaries that they've set.
I can understand how any loving GP having done so before being estranged, and continuing to do so having been estranged, would be conflicted when trying to decide whether or not they should continue with the financial contribution toward their GC's future.
She contributes to this fund so presumably it is not one that she set up and was set up by the child's parents. As I posted earlier, I can never understand why anyone would continue to receive gifts whatever they maybe, from someone they have estranged and don't want in their lives.
If these parents do not want her to be a part of theirs and their son's life then they shouldn't be accepting $3000 a year being paid into his college fund account.
If the parents consider her to be intruding in their lives they should refuse any further financial contributions, or is it OK if the 'intrusion' brings with it financial gain?