All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
If the people led in prayer stand on the right side of the Imaam only, and his left side is empty, then the prayer is valid and there is nothing wrong in this especially when there is no space. Indeed, the jurists stated that it is permissible for the people led in prayer to stand on the right side of the Imaam while his left side is empty. However, there is no doubt that the Sunnah is that the people led in prayer –whether they are men or women, two or more –should stand behind the Imaam because when the Prophet stood for the prayer, his companions would stand behind him.
For more benefit, please refer to Fatwa 81616.
Allaah Knows best.