The visual artist needs the window - so position easel? or other working items where the keyboards currently are . . . and start working from there. The blue sofa cushions - maybe hang them against the walls (they could function as pinboards?) - but I think you need something to deaden the sound - or your neighbours may hate you. Rugs on the floor and the thickest drapes you can afford (or improvise with blankets) for the window.

Hmmm . . . maybe artist towards the right-handside (door-side) of the window - trestles in L shape along the long wall, and a bit of the window to make 2 desks - and musician's stuff occupying the wall adjacent to the door and into the centre of the room? Everyone gets a shelf each in the cupboard . . . and a dedicated space in the room?

Could I suggest that guitars need to be hung on the wall somehow when not in use to allow clutter free space when utilising the computers and the easel.

Create an L-shaped desk/bench with the tressles as suggested by susan_66 with the desktops toward the corner to allow the artist to use the end for art materials or sewing machine (which would need to be put away underneath after use unfortunately).

Keyboards could perhaps be put against the wall near the door, or else hung similarly to guitars until needed.

I think the key here is for each user to be considerate of the others by stowing away their items after use so as to keep the area as usable as possible.

Good luck!!

Thank you so much for your ideas! We moved the trestle table along the window which made a huge difference. Just needing a rack that will be able to organise all the guitars. Any ideas for cheap curtains and rugs? Maybe the tapestry will help block the sound on one of the walls?