It is permissible to offer voluntary prayers in congregation, and to pray on hasir (palm-fiber mats), khumrah (small mats), cloth, and other pure things
Abdullah b. al-Mukhtar heard Musa b. Anas narrating on the authority of Anas b. Malik that the Messenger of Allah (ﷺ) led him, his mother or his aunt in prayer. He made me, stand on his right side and made the woman stand, behind us.