The three and 4 team tiebreaker is record against all teams tied. Nebraska and Northwestern are in a virtual tie with records against teams they could be tied with. After the initial multi team tie break is settled, the team with the best head to head against all of the teams in the tie will be the highest seed, and so on down the line. As I stated Nebraska and Northwestern are pretty much tied with their win/loss against the teams that are tied. When two teams are tied, it goes to head to head. Nebraska will get in before Northwestern.
Also, Northwestern is not beating Maryland at their place. Nebraska will play in the Big Ten tournament, as I wrote before is a "virtual lock".