What seems to be missing, Pip, is any semblance of an acceptable source on any of the children't profiles other than William. Even Nigel himself, is a bit short on sources.
Unfortunately they are relics from the period when WikiTree allowed anyone to download Gedcoms of any size and from any period in time, many of which contained dubious profiles like these.
Doubly unfortunately there are far too many of them and these Mowbray profiles may have to wait in line until someone has the time to do some in depth research into the Mowbray family.