Various tiebreaker scenarios:
Despite having a loss, Wisconsin is the ONLY team that currently controls their own destiny to the B1GCG.
As mentioned in the OP, the three undefeated teams do not play so they could all finish 9-0. In that case the relevant tiebreaker would be cumulative league record of league opponents. Indiana probably loses on that because they have what appears to be the easiest schedule.
That said, none of the undefeated teams technically control their own B1GCG destiny because they need some outside help.
Illinois has a loss to PSU and plays Oregon this week. If they beat Oregon they'll still need some help. The clearest path would be for IU to lose a game. That would get the Illini into no worse than a tie for 2nd place and the tiebreakers might just work for them.
I believe that Wisconsin controls their own destiny. If they win out to finish 8-1 that would give PSU and ORE each a loss. Wisconsin would be no worse than tied for 2nd (behind IU) and they'd have the tiebreakers over PSU (H2H), ORE (H2H), IL (record against common conference opponents), and tOSU (record against common conference opponents).
Ohio State needs a Wisconsin loss. They also *MIGHT* need an Illinois loss.