My take is that the subject of the verbs is 'some' or 'those', and the best forms are:
"Some of us actually got to spend their vacations in a little more special way than others."
"Some of us have tried to hold on to their old ideas and the result was nil until they let go absolutely."
"Those (of you) who want to join the chorus should sign their names on this sheet of paper."
However, I think 'our' in the first two and 'your' in the third are acceptable. Writers of pedantic style guides might worry about this. I don't think the rest of us spend our/their free time agonising over it.