My family invited FI's mother and grandmother (and an aunt of his also came) to the shower they gave me two weeks ago, and next week FI's same grandmother is giving me a shower which FI's mother, the same aunt, my mother and my aunt will all attend again. (Yes, I know you're not supposed to have overlap, but here we are. Apparently the families think it's fine if you're close enough relatives.)
Is it OK to wait until after that one to make sure to include any additional gifts they may give in the note?
His family's gifts at this shower I would consider average, not small tokens.
ETA: What about combining thank you notes if they will not be attending the wedding, but have already sent a gift?