Last I looked there were more than two members in the council, and also USSR hasn't been a member since 1991 if I recall correctly. Anyway here's the current list for you convenience: https://www.un.org/securitycouncil/content/current-members

If the bylaws of the security council contained the risk of exclusion or at the very least loss of veto, I think both the US and Russia would more carefully contemplate the cost of the invasions they are guilty of.