Asking others to donate in your name in lieu of giving you gifts is a fine idea.
My extended family discussed this several years ago and decided not to do it. They argued that choosing others’ charities for them and donating in their name is not always a welcome gesture. Even though I’d been the one to suggest it, I had to respect the fact that my brother (for one) said it wouldn’t feel much like a present if he just got a card saying money had been sent to some charity I picked.
Before you all jump on my brother, he said it would be fine not to send presents at all and fine to go ahead and donate to the charity of your choice. Just don’t confuse the two, he said, and try to make your donations do double duty as an unwanted gift to relatives, as if you were simply advertising your donation.