Join Date: Nov 2000
Location: Nashville -Past DL Plat, FO, WN-CP, various hotel programs
Programs: DL-MM, AA, SW w/companion,HiltonDiamond, Hyatt PLat, IHF Plat, Miles and Points Seeker
Posts: 11,405
Hopefully you put their FF number into their reservations. If so - everything at this point is the same as if they bought them.
Yes, you can do the 4 upgrades with them... at T-24 when you/they check in. Just pay with YOUR credit card.
And - congrats that you are going to use those upgrades for the kids instead of yourself. Keep in mind these are only good for ONE FLIGHT SEGMENT. If there is a connection, they need another.
Also, if traveling together, no need to do all 4. Do a couple or whatever works and save a seat..; assuming one/two of them will be sitting in middle seats anyways. Maybe.