My questions are:
1) Do I understand correctly that the professional class depends on verifiable past experience in one of the 38 categories, not necessarily on having a job offer in that field in hand? In other words, would I be accepted for my experience even if I'm more likely to find work in a different (though related) field?
2) Under the provisions for "substitute evaluation" or otherwise, would it be beneficial to me to indicate that both my wife and daughter are Canadian citizens?
First of all, although very late, I am sorry for the loss.
1) Yes you do. You must qulify under one of the listed jobs regardless of having a job offer from a Canadian employer.
2) If you can prove the relationship, that I suppose you can, it would be beneficila to say your wife was and your daughter is Canadian citizens.