I agree that it's tacky. We've had family members who give to THEIR pet charities and tell us that this is our Christmas gift. Just don't bother to "give" a gift, for crying out loud! (At least your idea gives them a choice of charities...)
I got excited when I found out one year that they donated to the art museum we took our kids to. I guess I misunderstood the donation because I thought that they bought us a family membership. Nope. It was just money they gave.
We never got any notification from the charities about receiving a donation in our name. I guess I just don't get the idea that this is a gift...
I do think that giving money to charities in the name of a deceased person is absolutely fine, unless the person who died specifically didn't like that charity... that is entirely different than a Christmas gift.