Eh, I wouldn't have two kids with the same namesake. I like too many names for that. I know a lot of families who use "
Lee" for all of their kids' middle names, and that makes me groan. I would ask if he wanted
David or
Dafydd to be his first son's name, and use one over the other.
Anyway, I like
David Royce McKendrich, if
Royce and McKendrich are family names (which it seems like they are). Are you intending to call
John Peter "
John Peter"? I like
John in conjunction with other names like that, and
John Peter's nice. I don't think
John Peter Dafydd flows very well, personally, but there's nothing wrong with it.