Dear Florence and Aveline
If my DH did either of the things you describe, I would simply tell him that if he can do it better than me, then he can damn well get on with it.
Especially whilst hoovering up the Christmas tree needles!
Florence, if this is the only area of life where your DH undermines you, then he is probably jealous of how well you get on with the grandchildren.
It might help if you and he found some activities that he does alone with them.
If he has always had a tendency to undermine you, I don't suppose telling him how rude and inconsiderate this is, will do the slightest bit of good at this late date, but you could try it.
This year for the first time ever when we were putting up the tree, I told DH I could not be bothered with his usual complaints about the fairy lights. Either he just got on with it, or he let me do it, and made no comments about the result (which would have been awful if I had done the job).
IT WORKED he put them up without a single curse. Now why did I not try that simple remedy years ago?