How can we perform ablution and pray 'Asr prayer if there is not enough water for all members of the group (six people) to perform ablution, where the water is sufficient for two to perform a complete ablution and for four to perform ablution only for the obligatory parts?

If the water is owned by one person or a group, and it is sufficient for some of them to perform ablution but not others, then those who can perform ablution should do so, and the rest should perform tayammum (definition). If the water is owned by everyone and is not sufficient for all, then no one has the right to monopolize it. They should value the water, and pay the usual price, or cast lots for it if they do not have money. If some of them have money and others do not, then the affluent person should pay the price to whoever wishes to sell, and some may donate their share and perform tayammum. If the water is shared by two people and is only sufficient for one of them, and both are affluent and their ritual impurity is of the same degree, they should value the water, and whoever pays the necessary price takes exclusive possession of it. If their ritual impurities are of different degrees, the one with the greater impurity takes exclusive possession of it. If both are destitute, they should sell it and divide the proceeds. If one of them is affluent, he must pay the price for his destitute partner's share, unless it is needed for drinking.