Is what the friends did—burying the human skeletons that appeared after the water receded from the cemetery—correct, and do they sin by missing Friday prayer to do so?

Whoever finds a deceased person or a part of one must wash, shroud, pray over, and bury it, unless this has already been done, and this applies if the deceased is a Muslim. If the deceased is a disbeliever, they should be left to their own people. If their people are not available, Muslims should bury them after wrapping them in something.

Burying skeletons is correct, but abandoning Friday prayer is a grave mistake; Friday prayer is obligatory, and abandoning it without a legitimate excuse is a great sin. Burial is not considered an excuse for abandoning it if it is possible to combine both matters. They must repent for what has occurred.