The formation of the LLC could be for ease of management & for estate tax reasons. Best case, they engaged an attorney to write an operating agreement that will help the family manage and use the property over the years, maybe even generationally.

The expenses could be partly deductible - i.e. property taxes and potentially interest. Should not be on lines 1& 2, though. Should be on Sch K in the other deductions section. Maintenance & other expenses would be nondeductible if the property is used only personally.  Forming an entity doesn't change the nature of the expenses, which have to follow the use of the property.

If it has property taxes or other federally deductible items to report, then 1065 is required to be filed, but even if not required, could be worth the expense if it forces them to account to each other at least annually for contributions made & expenses incurred, assuming the capital account section is completed.