The other hokage can help without getting themselves hurt...although Tobirama hasnt shown many feats, hes still powerful, Hiruzen is one of the "gods of shinobi" and Minato's never really been touched before. They'll be fine.I think it will be as simple as...
Madara vs Hashirama.
Obito vs Sasuke and Naruto.
The rest would just end up getting hurt.