This marriage seems too early for this family but is in the St Just records - see Lanyon folder
heir Living 1509
A William Lanyen was an overseer of John Rashleigh's will, which was written in 1578. It may have been a son of this William, in which case he would have been John Rashleigh's brother-in-law, but no relationship was mentioned.

All the children below are from a members entry to FamilySearch so may not be reliable.