"The Adult Mother & Father do not sing solo, but their parts are equal in size to the supporting characters, and actually appear onstage more often than Isle and many other characters."
Unless they make changes from L.A. due to casting Marlee, then, yes, her part would be fairly small in this particular production.
As previously mentioned in this thread, the Adult roles in L.A. were split between hearing and deaf performers. The deaf actress played Melchior's mother, not Wendla's or the schoolteacher.
I could see them possibly having Marlee play the schoolteacher, too, but I hope they will continue to use a hearing actress for Wendla's mother. Having a mix of hearing & deaf performers share scenes is part of the point of this production.