Do you need to maintain the current closet space? Also do you wish to keep the private WC? Will the budget support relocating plumbing? Are there any windows?

Do not need to keep current closet space, we could do with less space if well organized. We would like one walk in, opposed to the current two. Do not need to keep private WC. There is a large window on the back of the house over the tub. Yes we can move plumbing if needed.

Take out the tub, put a wall with a pocket door. Voila! Exercise room! Build the shower forward to make it bigger.

Remove tub and put shower there. Remove vanities and put double sinks in an "L" where right wall is and where old shower is. Put a door to closet located on right, where the current vanity is, and close off other door. Move right wall of closet on the left to abut/share the wall with the closet on the right. Add a door to where the current left vanity is, to access your new exercise room.

The benefits are that you wouldn't have to so a whole lot of plumbing modifications since the shower would now be where tub is, and vanity would now be where shower was (or at least close by).