I’m a stinkwad stickler for rules of etiquette
Emily Post says a short note is all that’s required.
That being said, I would never expect an acknowledgement.
When my mother died, I sent handwritten notes to family. Everyone else got a “thank you for your kindness and expression of sympathy during our time of grief” card that is pre-engraved/printed and available from most funeral homes at no charge.
UT~
I once made a donation to a fund set up for the kids of a college student. He was working nights at a 7-11 and a robber shot and killed him. A local DJ, where I was living at the time, started the promos for this fund.
A month or so later I got a very nice little hand written thank you from the family. It was the last thing I would have expected, considering all they were going through. Lovely, but they didn’t have to do it.