I would add a second 24inch sink with storage in the vanity if you can give up the space. I’m no pro but I have done a few bath renovations. I don’t think changing to a shower would save space because it’s a standard tub and the positioning would not provide much benefit in that layout. Just my opinion!

I meant if you can give up the closet space.

I would take out the closet and replace the vanity with a 52" double sink vanity, this way there will be more storage space for small items (cosmetics/hair products) for your daughters in the long run. Also, I agree with r2logan, changing from a tub to shower will not give you more space. However, a shower will be easier to clean and gives the bathroom a more modern look. You can add in a niche for shampoos and shower gels. If you are considering changing the vanity, having a full bathroom renovation at the same time might be a good idea!

Hope this helps!

Not too long ago my DS redid her girls' bathroom. Instead of a double sink vanity, she put in a new, longer vanity with one sink offset to the side closest to the door. That way they have more countertop space for their toiletries and hair tools, etc. And they have a whole stack of drawers under the non-sink side which is great storage for toiletries, make up and such. She put in a marble countertop, but I probably would go for quartz or granite in a kids bathroom. She bought a silicone mat that is pretty much always left sitting on the counter so that if they put a hot hair tool down it will not burn the counter. For the mirror, she put in one large mirror that spans the entire counter area. She did take the tub out and built a shower instead. The girls appreciate the extra counterspace, and for them it was a better choice than a second sink. The age difference between the girl's is 8 years, so they installed a hand-held shower fixture on a bar so they can adjust the height. But even if your girl's are close in age and height, a hand-held on a bar is a great choice because it can grow with them. It is also a good tool for cleaning the shower.

Looks like you have about 9'1" feet to work with (109"). If you use the minimum clearance of (30") for the toilet you have 79" left to work with. Most people hate showers that are only 30" wide. If you build a shower that is about 34" wide, you will have 45" left for the vanity with one sink. If you do a shower that is wider or skinnier, just add or subtract from the vanity width available. You might want to see if it's feasible to have a medicine cabinet on the wall closest to the door with electrical so they can charge toothbrushes and such. Depending on feasibility and budget, you could also do lighted, mirrored medicine cabinets, with electrical inside, spanning the width of the counter. Those are expensive. The vanity will have some storage, and you could add an over the toilet cabinet for extra TP and other necessities. DS installed hooks on the wall for towels instead of a towel bar. She did clever thing and sewed loops on the towels so they were easier to hang.

Little tip I never heard of before DS's contractor suggested: when they built the shower, they put a little toe rest for shaving legs. It's like a small niche. I've also seen pictures of little shelves serving this purpose.