I have a 61/2 year old grandson who is torn ...

I'm sorry to hear about your situation.

With that said, I found an interesting forum that talks about raising a child while the father is in jail. It may have some helpful information for your specific circumstances, so it may be wise to read the information over and pass it on to your daughter. You can see the website here. 

Good luck. 

It's perfectly normal and natural for your daughter to be absolutely furious with her husband, drugs can totally destroy a family.  IF, and it's a big if, your grandson's father is making progress in his rehab/treatment, has realized his mistake, and wants to see his son I don't see the problem with it.  If his father is a real loser, your grandson will realize this on his own, kids are smart like that.  Keeping him away from his father is going to do nothing but damage to your grandson and your daughter needs to let up a bit, maybe supervized visitation for a while is a good way to start working him back into her son's life.

First off the Grandparents had no right to take the child to see his Father, Then tell him to lie to his Mother. They are messing in the mother's rights to raise her child. And if it were me, that would end the Grandparents unmonitored relationship with the child. He's in jail for crime, So, Why make the child do the father's mental time?