Welcome! This forum has a treasure trove of great info – Scouters helping Scouters! Just a heads up, though - all content, information, and opinions shared on this forum are those of the author, not the BSA.
Once a MBC is connected to the scout, I generally have to go into that connection and add any additional MBs in that connection. I’m surprised that you were able to use the invite counselor interface to connect the MBC to the scout twice.
The other possibility that leaps to mind is that the five scouts haven’t “started” the Family Life MB in Scoutbook yet.