What is the ruling on zakat for money collected monthly with the intention of purchasing land or a family resting place, and how is it to be disbursed if it becomes obligatory, and is it permissible to spend it on building mosques, Quran memorization circles, and sponsoring orphans?

As long as you have not yet purchased the land, each partner must consider his share of the money. If it reaches the nisab (threshold) by itself or with other assets, and a hawl (full lunar year) passes over it, then he must pay a quarter of a tenth (2.5%) as zakat. Mixing of assets does not affect anything other than livestock according to the majority of scholars.

The hawl considered is the passing of a lunar year after the money reaches the nisab.

It is not permissible to spend zakat on building mosques or Quran memorization circles, because these are not among the categories for zakat expenditure. It is permissible to spend it on a poor orphan or a miskin (needy person), but not on a wealthy orphan.