give them something to be jealous of. build the love stronger among the two.. once they see you're happy together, and there's no other place you'll rather be... it makes them mad & get under their skin... and they'll leave you alone. :)
Ignore them and cut them out of their lives as much as possible. If they really love each other and the relationship is a healthy one, then other people's opinions shouldn't matter. Make sure you ask yourself though if jealousy is really the reason people are interfering. Could it be that they're trying to protect you or him from what they think is an unhealthy relationship? I'm not saying it is, I'm just saying to be completely sure of their intentions before you kick them to the curb.