Actually, if we are a Christian family, it's better to say Grace aloud together.
Even if we are not a Christian family, if we can start a habit to do this before our non-Christian family members, it also good. However, I would suggest in this case, Christian sit together and say Grace in a silent tone and make it short, do not give pressure to those non-believer.
[size=small]I encourage you to say it aloud at home and if possible to so outside as well! [size=small]]it's a good testimony for non-believers and you are also setting a good example for your kids, to remain thankful for whatever that's in front of us! we sometimes hold each other's hand while we are saying grace!