Sounds like you've gotten good advice already. I would ask the purser's desk if it's okay if just your husband attends the lifeboat drill -- it's a ridiculous hour to have a drill even for adults! Or you could just have your husband attend and when they call out your cabin number to take attendance he could say that you're both there (they only ask one person in your party to say "here" and to state how many people are in your group.) However, don't let them know that I suggested it!?! Make sure, however, that you do have an infant's life vest in your cabin -- you can request it from your cabin steward.
If you haven't already, read the articles I've written on this site about cruising with an infant. We took my son last year on two cruises when he was 7 and 10 months old and we had great times.
Luisa Frey Gaynor
Family Cruise Editor