Well, there are a couple mistakes, so the sentence is not entirely correct in Spanish. La familia se reúne para cenar en torno a una mesa preparada para tal fin. The family gathers for dinner around a table which has been prepared for this purpose. No one would ever say this in spoken conversational Spanish. We don't use the grammar, vocabulary or diction.

La familia se reúne para cenar en torno a una mesa preparada para tal fin. The family meets for dinner around a table that is prepared for this purpose - It means that the different family members meet for dinner around a table that is prepared for this dinner, this kind of sentences normally refers to important meals, such as New years eve. - La familia: The family - Se reúne: meets - Para cenar: to have dinner - En torno a una mesa: around a table - Preparada para tal fin: the table has been prepared for this purpose (the dinner)