The second invite, especially for a marriage ceremony, is sent to Lord Vishnu and Maa Lakshmi. In events like weddings or housewarmings, blessings of the duo are especially important as they both bless the couple with love, abundance, balance, and more.
It is believed that Lord Vishnu makes sure that the ritual or event is protected from harm, and Maa Lakshmi ensures that there isn’t a deficit of anything in the event. Maa Lakshmi brings abundance of money, happiness, love, and more, and thus the second invite is given to them.