Yes, group prayer for anyone or ones does work miracles. Yes, prayer (Mind) affectsmatter. This is scientifically proven. Through focused intention if you pray it can change internal and external conditions of life. Bhakti-Marga, loving devotion,  does have a big space for humble prayers. Whenever your body and mind is aligned through prayer or at deeper level meditation, you affect matter and circumstances.  Let prayer rise with all words of gratitude and surrender.