Andrew,
On the questionable line that you refer to, I think you raise several good points.
My suggestion, for starters, would be to pick one point (the Curzon wife, possibly?) and we focus on that connection. At this point, it is buried in this g2g, so I would suggest starting a new g2g where you connect it to that particular profile. In that post, you can lay out reasons and sources for why you draw your conclusions and ask for input.
This would give folks with an interest in those profiles, who are familiar with the sources, a chance to weigh in.
I'd be happy to help you think about how you want to lay that out, if you need it.
Are you familiar with our sub-project, "Category:Questionable_Gateway_Ancestors"? We have had many similar g2g discussions around these questionable lines and have removed a number of dubious connections. You may want to refer to those discussions as a reference for how you lay out your (Curzon) thinking.
Feel free to private message me, etc., if I can help further.