In astrology 5th house is taken for mantra sthana. The sub lord of 5th house is taken for this purpose. But in some charts, the sub lord may not be connected to the positive houses. Then it would be a problem.
In your case “Muneeswaran” or “Lakshmi Narayana” also gives good results. 5th cusp sub lord is Jupiter conjoined with Venus and aspected by Saturn and signifying 11th house. So you can pray these two. I can not say the family daity.