The teams are not allowed to compete. You would be allowed to split the ice in two and each team could practice in their own end. You cannot run a combined team practice. If you proceed with coaches as referees in a game, it is an illegal game and the USA Hockey insurance is voided as well as potential implications for coaches and players.
IX. Game Requirements
3. The following conditions shall constitute an invalid game:
a. When two registered teams occupy the same ice surface and compete without registered referees, with or without the clock and scoreboard, with or without coaches on the ice and without a completed/signed score sheet. Coaches and players for both teams are subject to suspension under rules II., B., 1 and 2. This session does count toward the maximum game count for each team.