Should we believe him?

Thank you ladies. Yes Silverlining48 GS did tell SIL who repeated the scenario with DD but said he (SIL) was not there so couldn't confirm. DGS visits he dad every other weekend Bluebelle. He really loves his Dad but at times has been reluctant to go. Good points Newmom101 will take that on board. The nail incident happened when he first went there so nothing was said...

Definitely believe him and speak to his dad. He is not speaking in vague terms he is being very specific. Children should always be believed in these circumstances unless you have absolute proof it is NOT happening.

If she's really sunk her nails into his head he'd have marks on his scalp, did no one check?

It's a tricky situation as you have no proof either way. However, if I were your DD in this scenario I would be requesting to my ex that DGS and Wendy were not left alone together, to ensure that there is no chance for these situations to occur. I would also be telling DGS that if anything happens again he is to immediately report it to his father. As well as that, I would be providing him with a cheap mobile phone to contact your DD if something does occur and he wants to go home, as you cannot guarantee his father will keep an eye.

It's far better to be cautious and over the top, than risk a child being abused, which (if this is true) is exactly what she is doing. Sadly there have been lots of occasions where people assume a child is making it up and when the person accused is a woman people are far less likely to believe the child.

Does he seem reluctant to go to his dads?

Surely the best thing to do would be to go and speak to Wendy?
If, as it should be, everyone is concerned with your grandsons wellbeing, then they should be able to have an uncomfortable but civil conversation, and sort out what is going on.

Does your grandson live with his father and ‘Wendy’ ? If so then I think his dad needs to know as it may escalate or does he just visit ?

Could you encourage your grandson to tell his Dad while you are there to support.

Difficult but in my opinion your dd should say something to the father about what your gs sAid. If this is going on it needs to be stopped. If nothing is done then your gs will not feel able to tell if anything else happens, what’s more, he will feel let down by all the adults in. His life.
I said something once, it wasn’t mentioned or followed up,more is the pity.