Oharas, You are under the same rules in MS as you are in HS if the MS is a OHSAA sanctioned team. You may coach them since you are the HS coach and they are MS students subject to these rules cut from the OSHAA rules which limits the number of players from their school:
4.21) The number of interscholastic fast pitch softball players from the same school
on a non-interscholastic squad is limited to four on the roster of that noninterscholastic
squad. A roster is defined as all the members of the entire
squad on that non-interscholastic squad.
Note: Graduating seniors who are participating on a non-interscholastic fast
pitch softball squad after their final interscholastic contest of the season in the
sport of fast pitch softball are exempt from this limitation.
4.22) There is no limit on the number of fast pitch softball squad members from the
same school participating on the same squad during the period June 1-July 31.
4.23) A player may continue to play with a non-interscholastic squad in a national
qualifying tournament in excess of the four player limitation after July 31
until the squad is eliminated but no later than Labor Day.
4.24) Non-interscholastic participation includes tryouts, training, practice and
competition.