I would suggest that you visit or write the Evart Public Library/Museum (P.O. Box 576 Evart, MI 49631-0576) for information about the McMullens. The McMullens lived in Evart Twp and I think they had a lumber camp and farmed. I'm pretty sure the library has some genealogy information about the family.
The Library/Museum has some paintings by a McMullen descendant that were painted in the 1950s. I think he was reasonably well known. There may still be some family members in the area. Elna