I'm having some difficulty getting my 3 remaining villagers(all of which are female) to the master builder level. I've built one hut and repaired the other one and am working on the sewing hut which is around 91-92% complete. All 3 females are adept builders, the eldest is close to becoming a master builder but I don't think she or the other two will make it before the hut is complete. And I need 3 master builders to open the crate on the beach.

EDIT: Forgot to mention that my eldest villager is in her early 50's while the other two are, I believe, in their 30's.