If you’ve had a child who died from SIDS, obviously you’ve been through an extremely traumatic event. It’s only natural for you to be over-the-top worried for any future children you have.
Doctors don’t know if the risk is elevated for siblings of a child who died of SIDS. But they do believe that one gene mutation is not the cause for all cases of SIDS (source). They do wonder if there are genes that predispose children to SIDS when combined with other risk factors.
There is no way to completely eliminate the risk of SIDS so you’ll still undoubtedly feel worried about it happening again. The best thing you can do is to educate yourself about what you can do to reduce the risk as much as possible.