Spouses both with Cancer???

I have a sister who is fighting a deadly cancer (Mantle Cell Lymphoma) and about the time of her fifth chemotherapy treatment they found that her husband has colon cancer. He had surgery and then emergency surgery and lost about 24 inches of colon. We don't know yet what other treatment he might need. And my sister has a long ways to go in her treatments yet. But my concern is whether or not something in the house they had built in a new development is causing the cancers and if so, how long until their two teen sons have cancer of some sort. I found out recently that after the huge kitchen had the tiles put in for the large counter tops, my sister decided not to take the time to "seal" the grout in them. How can I find out if this is a possibility and if not where do we begin to have that house tested for a possible cause? My sister is 45 and her husband is 50 and it is taking it's tole on the whole family to see them suffer like this.