Thewlis i'm happy with,he has great hands, good engine, lots of speed etc. He hasn't shined because Tai is more of a defensive centre than a strike centre. If he was playing outside of jake Wardle, Tim Lafai, Hiku etc He'd be well further up the try charts, I'm happy with him.
Musgrove has played bog standard low minutes this year, I know Burgess rates him higher than his actual displays though, so this will keep Max Wood from playing more games than him. Wood has a much better engine, better skills and a slightly better impact than him......but Musgrove gets the nod every week over him, bit of unjust favouritism there i think.

The rule that was introduced in 2024 with the allowance for a 3rd Marquee Player specified that the player had to be Federation trained, so Vaughan wouldn`t have qualified to be used in that role.

You would wonder why Tai has had so any games if you looked at his attacking/skills & stats but to balance things up we ought to mention that he does flatten a few & at times it provides a great lift for the side. Not many run through Tai & most come of worse. Big Sam obviously puts defence high up on his priorities when picking a team.
We also seem very obsessed with using our backs to carry the ball up, presumably to rest our forwards for defensive work, and he's pretty good at this too when it is very very tough.
Lindop, obviously, will be a better all round centre in time.

I thought as we had Williams on Marquee as Fed trained we could have 2x overseas marquees if we wanted?

Yes we could have 2 Overseas Marquees, but they count more on the Salary Cap.

A home grown Marquee only counts for £50K on the Cap.