I would highly recommend that you look into AFM Safecoat which has some great low-voc sealers. Specifically, look into their MexeSeal product since it's also SCS Certified and can be used on various interior surfaces.
For cleaning marble, take a look at Howard Products which manufactures various cleaning products for different types of surfaces which really work great.
- They carry a line of natural cleaners called "Howard's Naturals" derived from vegetable ingredients that are non-acidic and non-abrasive for cleaning granite, marble.
- They even have cleaners for stainless steel surfaces (non-pretroleum base).
For more information:
Read "I have marble bathroom tiles that are quite heavily soiled with soap scum. Can you recommend a nontoxic but effective cleaner/sealer?" a Q&A answered by Molly McCabe.