Salfordlad has it, of course.
There you have it from the lad from Salford, Either move the obstruction and then replace the balll in play after the inevitable movement or lift the ball, move the obstruction and drop a ball depending on whether ball in play is touching the course. I would suggest that the player's ball is inevitably going to be touching the course. If it weren't, you would have the situation of one spherical object balanced without any other support precisely on top of another. How likely is that? Whether the two balls are touching each other or not, the player's ball will be touching the ground It doesn't matter whether the two balls are touching each other, the upper one will in either case be touching the course which means the relief procedure has to be to remove the obstruction first and then replace the ball, dealing as is likely with the problem of the lie.
He is not obliged to take relief from a movable obstruction and so yes to the first part.
I don't see any problem in his hitting the stray ball first. it is not his ball in play; he is not hitting it in the belief that it is the ball in play; he is simply hitting a movable obstruction in the process of making a stroke at his ball in play. (Why he would do so when he could take relief is another matter). No penalty then, though the outcome might not be good.
All open to challenge of course!
Does 'in play' have anything to do with it? Most 'wrong balls' on the course aren't in play but they are still wrong balls? (Otherwise the wrong ball rule is a nonsense)
So, what about my thoughts in #26?
Eg. Player knows (can see) 'other ball' is there
Other ball is in very close proximity to players ball.
Whilst 'other ball' is a movable obstruction, it is still 'a ball' (ie a wrong ball which you are not allowed to make a stroke at without penalty
To hit own ball, player knows they'll have to also hit other ball - ie can't hit own ball without intending to hit 'other ball' as well
So is the player making a stroke at a wrong ball? Should there be a penalty.
Ps - only asking, not arguing.