How can I find a marriage license? Ancestry.com?

I'm not sure about Ancestry.com, but if you went to the county courthouse and the church where the marriage was supposed to have happened and there was no record, then I'd say it looks slim that your grandparents were legally married. I'm not completely sure, but I think back then "commom law" marriages were acknowledged more, so maybe that is what happened. If you can't find the legal records, then no website will be able to either, so save your money.