Is it permissible to pray two Rak'ahs in congregation - with an Imam - and dedicate their reward to a deceased person with the intention of multiplying the reward, or must each individual pray them alone?

The issue of dedicating the reward of acts of worship to the deceased is a matter of scholarly disagreement. However, what is agreed upon is that the deceased benefits from supplication (du'a), seeking forgiveness for them, giving charity on their behalf, and performing Hajj and Umrah (definition) for them. It was not the custom of the Salaf (pious predecessors) to dedicate the reward of acts of worship to their dead; rather, they performed these acts for themselves, while supplicating and giving charity on behalf of the deceased. According to the view that permits dedicating the reward of prayer, it is permissible to do so individually or in congregation. However, regular congregational performance of non-sunnah (definition) supererogatory prayers is a reprehensible innovation (bid'ah makroohah), and it is better for each individual to pray alone.