<human>: Can you condense the text into a few key points?

Probably too much backstory:

My boyfriend's grandfather (90) passed away somewhat suddenly on Sunday. Viewing is tomorrow evening; funeral is Thursday. We're on the east coast; the majority of his family (and his grandfather's funeral) is in the midwest. BF's brother almost immediately drove a few hours south to our place, stayed the night, and they started on westward drive to their family yesterday (Monday) morning.

I did not come partially because we have a dog and a new kitten; at that time I might still have been hosting his sister tonight (Tuesday) for a night while she got a connecting flight, and because I don't have enough vacation time at the moment to take a whole week, nor do I think my job would have been that supportive in letting me take a week without notice since the death was in my boyfriend's family and not my own.

Anyway, I'm looking for advice as to the most appropriate way to share my condolences with his family. His grandfather's obit says to make donations to a charity in lieu of flowers, which I'm fine with doing, but I'm not sure it expresses to his family that I'm sorry for their loss. 

Is my only other option to send a card?

It's also a little strange because at the moment BF's parents don't really have a permanent address; they retired a few months ago and have been traveling/haven't decided where to settle down (they're a military family and have lived all over). So at the moment they're staying with his aunt for the funeral, but I have no idea how long they'll remain there.

Any advice?
<bot>: Boyfriend is in his homestate for the week for his grandfather's funeral; I was unable to come. What's the best way to express condolences when the obituary says to make donations instead of sending flowers?