However I stand by the fact that I think it is sad that people see so many negatives behind GP wanting to spend time with her DC. I'm sure most GP who offer this are thinking as well of offering the parents a break and some time off. This break or time off may not be wanted at all, and doesn't need to be taken, but that doesn't make the initial offer not well meaning.
I'm certain many GP do - my mother does, definitely. My MIL has never had the least interest in DS visiting, she's not even that enthused about DS going up with DH because really she'd rather have her son to herself - it makes me sad. I was really chuffed that she started showing more of an interest in him this year, now he's less of a baby and more of a strong individual in her eyes. So I accept your point. GP are really important, and though my MIL drives me crazy and she's not actually hugely interested I foster the relationship DS has with her and with my MIL in his own mind, so he's interested in them and always delighted to see them, which now pays dividends in them finding it flattering and making more of an effort. It's important for children to feel part of a wider family, IMO, and DH being an only child, his father being the same, and his mother barely on speaking terms with her siblings makes his GP all the more essential to that sense of family roots. No argument here.
The problem is, the point that lots of GP want to offer the parents a break just doesn't apply to this situation - the OP has been enormously pressured and even harangued for not agreeing to a large chunk of time being spent with GP her son really doesn't know that well at all, when he's barely more than a baby (and at 18 months, was pretty much still a baby, when an overseas holiday alone was demanded of her). That is not in any way, shape or form about offering her a break - it's about wanting to be in sole charge of a small child. She's offered visits at either address with her there too, and that isn't good enough. It isn't about her, or the child. If it were, the visits could begin when the little boy is ready to make them, and not when the adults feel they would get something from it.