Maddie - maybe she (DIL) feels insecure and jealous as she hasn't a close relationship with her parents, and so by isolating your son they are 'in the same boat' and reliant only on each other.
Regarding 'he believes in the "education and career isn't what you should be doing propaganda" put out buy the WT' - my head wants to say, 'get the WT to support/subsidise his salary then'. I've found that, one way or another, most of US (me included) are still having to compensate (wrong word, but I know what I mean, lol) the WT (whether time or money) just to maintain relationships with JW relatives.