I do hope they join back with the Catholic Church.Or maybe the bishop will allow them to found a new smaller parish.Don’t know anything about the group they want to join, but they would be better off with the Polish National Catholic Church.Their bishops and sacraments as far as i know are licit,and members of their church may take communion in a Roman Catholic Church, and there is talks between them and Rome with possibly returning to us.There is information on the Polish national Catholic church on the web and they have a website.