Both legs my uncle's were amputated due to serious diabetes. Do we have bathe them as Janazah and also perform Janazah prayers.

Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions. The amputated legs do not take the rule of the whole body of the dead person. So, they are not to be washed and no funeral prayer should be performed on them. Actually, they take the rule of anything that gets separated from the body of a living person. So, they should be buried in respect to the human being. But it is not from Shariah that people wash these legs, pray on them, or follow their funeral. These legs should also not be kept until the death of the person from whom they were taken and buried with him. Allah knows best.