Grr, just noticed I must have been even more confused than I thought - I was actually thinking Peter was son of Thomas, but wrote William
Anyway, thx - yes, I think it becomes much clearer if you remove the text in brackets re Peter's dad, ie:
The elder son, Robert Smytheson of Thornton Watlas, who married – -, and had issue … an elder son, viz.:
Peter le Smytheson ...
It's just that suggestion/reading that Robert Smytheson might've been Kerperby William's son, but that's not the author's style as I've seen elsewhere, so I think you're right - Peter is Robert's son.
It's also that line
"and had issue (together with two other sons…" that kind of threw me. Wonder if the issue in question was a daughter or daughters - just seemed a strange way to put it. Anyway, although I mentioned verifying all this, I pretty much will have to take the author's word for it here though, given the absence of parish records and my lack of Latin / OE skills for where records do exist.
Thanks for the link too, bookmarked.
EDIT: Actually, no, that issue line makes sense now I think - the two 'other sons' are Peter's younger's brothers who just get a mention in passing...