I would like to know are there any rules regarding the formality or informality of the Purim seuda. I personally think it should be like a Yomtov meal with appropriate food, everyone seated around the table, becuase I’ve seen that in other houses. My wife however prefers (probably to accomodate her non religious siblings, and their kids) dishes like spaghetti bologniase or meat grilled on the barbeque with pitot and chummus and such, which make it much more informal, and people will move around and not be seated at the table. What should be the rule?

The Mishna brura on Hilchot Purim (695:1:3) mentions that it is proper that a person wear Shabbat clothes for Purim and when a person comes home after reading the megilla, his table should be set and his bed made and candles lit.. These issues are similar to requirements for "Kavod Shabbat" which require us to wear nice clean clothes on Shabbat and to have our table set etc. On the other hand, the requirement of the meal is a less rigid atmosphere because this is the time when most fulfill their requirement of making themselves tipsy enough not to differentiate between "Arur Haman" and "baruch Mordechai." Of course the meal should begin with divrei Torah to set an atmosphere of chag not of frivolity. Each family with children and guests has to find their way of keeping the halachic requirements and at the same time keeping the children happy and part of the religious experience so they have a positive and memorable Purim. May you and your family have a very happy Purim.