There are three trees on Ancestry, which is probably where your library lady looked, as the baptisms aren't online, and online trees are to be used as guides only. But I can only access one of them. None of them show spouses for the other children. Joseph Boyce is shown as dying on 9 Jan 1810 in Plymouth, although I suspect this is probably the burial date. There are birth dates for all of the children, but these may be baptism dates. There are no sources.
I suggest you check this tree yourself in the library if you can't access Ancestry trees yourself, to extract any useful information, although no other detail is shown for the children. So it's back to the parish register.