What is the ruling on congregational prayer if some of its members pray standing and others pray sitting, and what is the ruling on the prayer of one who prays sitting while able to stand due to the lack of an available space?

Standing, when one is able, is a pillar of prayer, without which the prayer is invalid. If congregational prayer prevents a person from standing despite being able to, then it is preferable for him to pray alone while standing. If he can join a subsequent congregational prayer while standing, then he should delay his prayer and pray with that congregation while standing. Multiple congregations are permissible within the same mosque.