At the time of the founding of the leper colony on Molokai, leprosy was epidemic in Hawaii. Molokai was the least heavily used island at the time, and there was space available for the leper colony. The founders believed that it was important to keep the lepers away from healthy people, and the remoteness of the colony allowed this separation.

kalaaupapa

No, Bethany was not a leper colony. Bethany was a village located near Jerusalem in the biblical region of Judea. It is known for being the home of Mary, Martha, and Lazarus, who were friends of Jesus.

Possibly Molokai which used to house a Leper Colony.

Yes, St Stephens Green in Dublin was once a leper colony.