Fair rotation. Period. Major holidays — Thanksgiving, Christmas, New Year's, Fourth of July, Spring Break — rotate annually among the 4 families. Year one you get Thanksgiving, year two it rotates. No bidding wars, no seniority system, no one family hoarding the best weeks.
With only 4 owners sharing 52 weeks, the math works in everyone's favor. You get 12 weeks per year, and peak periods are baked into that rotation from day one. The schedule is set before you close, so there are zero surprises.