It sounds like you are in a very difficult position. This is going to take a lot of patience but eventually it could work out. For now acknowledge their feelings about him. Don't defend him right away. Find a compromise, any compromise, that your family is willing to make. That may not include meeting him right now. You may have to reintroduce this subject over time. Longevity is going to be in your favor. They may relent when they see the relationship has lasted. Any available compromises on either side should be acted on. Right now they may see him as someone with you for your age. You have to prove them wrong. If they like him enough to accept him they may accept the rest too. The one thing you don't want to do is push him on them. They have to come to terms with this on their own time. Maintain your relationship with them. Tell them you aren't going to leave him but understand their reservations.
Please press accept; this is the only way I am compensated