It looks to me as though the area you have got for your Jack and Jill - 1.5m x 3.7m , should be perfectly adequate for two ensuite shower rooms, one for each bedroom.
If you nicked an extra bit of width and made them 1.8 x 1.8 each, you might even have space for 2 bathrooms.
Personally I'd go for 800m x 1.7 shower trays back to back in the middle so that it would feel really spacious though a smallish room - ie make each bed about 2900 not 3000 wide, then you would roughly 1.7m x 900mm for a loo (corner loo?), vanity and whb in each one with a sliding door at the end.
That's not particularly tight, you just need to take care where you place the gubbins.
Giving a house several ensuites really affects the feel of the place.
Why not turn the main bathroom above in to an ensuite for Bed 3, or give Bed 3 a small ensuite shower room and make it a study?
Ferdinand