Mother, and 2 sister-in-laws = Boogie Boards - digital blackboards (http://www.amazon.com/gp/aw/d/B002ZE4TDI)

2 brothers = blow guns (http://www.amazon.com/gp/aw/d/B003NEVP36)

No idea what to get dad *got Dad (who's a motorcycle enthusiast) a portable electric tire pump he can carry in the side case for emergencies. Plugs into any car lighter socket. (http://www.amazon.com/gp/aw/d/B000GC9B0W)

or my little nieces yet... I'll be looking at the other replies for ideas!

Great thread by the way.