A floor plan with dimensions of the room would be very helpful. Also, can you show the layout that you intend to do for the new bathroom. I don't know that I can offer any advice without this additional information........

About your plumber saying "plumb layout is confirmed". That is a load of rubbish. It's fairly easy to move drains around (yes he might have to rip up some walls, but he can also do off-the-wall installations to avoid that). In a small bath proper placement is of the utmost importance!!! If you have the bathtub and shower next to each other that will be much better and then the glass separator idea should work. padmaramachandran's (see post above) setup sounds more reasonable to me as well (see first picture below). This is similar to your setup but as you have more space you could put in bath tub and shower where the picture only shows a bath tub. Also if you do it that way you could theoretically have a bidet or a wider wash basin (small double perhaps too). Example layout: Do you need a bathtub in the guest bath? If not you have a lot more room to work with. E.g. for a double wash basin and large walking shower and a bidet (2nd picture). Example of off-the-wall installation for toilet and bidet and a large walking shower. Finally if you ignore this advice and do it the way you planned ;) then I suggest you really thing about that glass separator. Doing it right will make a lot of difference (see 3rd picture). Good luck!

For the time being (and this IS only a temporary fix) try using a water based penetrating sealer on the grout. I stress water based, because solvent based sealers today are made to be "breatheable", meaning they allow moisture to transmit back and forth, while the water based sealers will repel water. You still need to address this in a more permanent manner (the glass door is a good idea, but it wouldn't hurt to remove the bathroom floor tile, waterproof the floor, and install a new tile floor), but this will help until you can afford to do what you need to do.

My partner and I picked tiles we thought would work but that we both hate (mostly the beige coloured ones inside the shower/steam room). There weren't enough of the blue tiles in the shop on the back wall to do whole shower. It's our fault and now we're wondering what we can do to basically change the beige mosaic tiles?Someone suggested tile paint, but I hear it looks terrible over the grout areas.Also niche shelves I requested for inside the shower room were not put in, which I really wanted. I'm upset they're not in and am nearly considering doing that wall again to get them in. Someone suggested glass shelves, though I'm not sure they're safe in a steam room?I almost want to do the whole thing again. 😩 It's hideous.