I believe your William Laval is the son of Jacinth Laval. I am descendent of William's sister Leonora. I highly recommend books.google.com for research. I have found tons of information about the family. Jacinth owned Lowndes Grove Plantation on the Charleston, SC peninsula for a short time when he was sheriff of Charleston after the Revolutionary War. It is still there today as a bed and breakfast, and a great site for weddings... I should know, I got married there :)
I just did a search for "william laval" on books.google.com. The first listing is a book which you can only preview, but has the marriage of William to a Miss Ward listed.
Lineage: Todd Crosslin - Marvin Crosslin - Theopa Laval Piester - Laval Piester - Caroline Laval Martin - Leonora Laval - Jacinth Laval
Regards,
Todd Crosslin