Answer: The need to translate the Haggada into another language is already mentioned in our halachic sources. (See Shulchan Aruch Orach Chaim 473:6 where Rama mentions that one of the early commentaries, Rabbi Yitzchak of London, translated the entire Haggadah for his wife and children.)
Many families in Israel share your problem because their children understand only Hebrew while their guests understand only English.
The right thing to do is to say the Haggada in its original Hebrew and supply your guests with an English translation to read while you are doing so. You can cite any additional commentaries, rotating between Hebrew and English so that everyone feels they are taking part.
It might also be a good idea to supply your guests with a transliterated version of popular songs like Dayeinu so that they can sing together with everyone else in the same language.