That would be "introduzem". From my understanding, although "apresentar" literally translates as "to present", it is usually translated as "to introduce" when describing someone introducing people, since this is the most common way to say that in English. However, "to present" is used exactly as it is in Portuguese in this sense in very formal English, eg. "M'lady, I would like to present Sir Charles Hollingsworth, Esquire"
idea is singular so with the possessive "seu/sua", it reflects that, not who is possessing. however why is seu/sua appropriate for 3rd/plural instead of "a ideia deles" ?