] Is it possible that Frederick is giving Isabella just enough encouragement to persuade her to break her engagement to James (which she'd love to do anyway, now that she's see they would not be RICH), for the benefit of not only James, but also Catherine and the whole Morland family?

As far as Frederick is concerned, I guess anything is possible. We don't know him and, frankly, I don't much like him at the moment.

But for Henry to be encouraging such a thing in order to prevent the match? Nah, I just don't see it. :-) While it is true that Isabella appears to be obviously wrong for James and the connection is not what I would wish for Catherine, I don't believe our Henry would interfere in this manner. It's just too underhanded and sneaky, not to mention painful to Catherine and James. It's more Thorpish than it is Tilneyesque. ;-)