Personally I think lag/afk sharing should spread units across multiple players. Example:
Units of 1st afk/lagger are shared to #1 non-afk/lagging elo player
Units of 2nd afk/lagger are shared to #2 non-afk/lagging elo player
Units of 3rd afk/lagger are shared to #3 non-afk/lagging elo player
There's a few extra situations that'll need to be handled though. Example:
If 1st afk/lagger comes back, will 2nd afk/lagger's units be given from #2 to #1 elo player?