What is the ruling on worshippers going to another mosque 18 km away under the pretext of there being more worshippers, and some failing to attend Friday prayer at the local prayer area, contenting themselves with praying at home?

It is not permissible to have multiple Friday prayers in one locality unless there is a need. If there is no need or necessity for establishing a new Friday prayer in this prayer hall, then it is not permissible to establish it. Rather, everyone must attend the first mosque and establish the Friday prayer there.