How to fix loose joints?

Wait for dry weather before tackling loose mortises. Old hide glue shrinks and expands with seasonal humidity. Knock the frame apart gently with a soft mallet. Clean off the crusty old glue and reassemble it with fresh adhesive.

The bedroom floor is really uneven in the old cottage and the wooden rail wobbles around every time someone walks past it, can it be levelled?

Those splayed feet are tricky to adjust without ruining the line of the leg. You want to avoid cutting the timber. Stick a small felt pad under the shortest foot. It absorbs the wobble and protects your floorboards.

Best wax for water marks?

Coloured beeswax blends out minor blooming on the finish. Rub it in sparingly with a soft cloth and leave it overnight before buffing.

Bought a mahogany one but the top bar is a different colour to the legs and the bottom sections, was it made like that originally?

Damp cloths sit directly on that top rail for hours. The moisture breaks down the original polish and slowly bleaches the timber underneath. Legs escape this daily soaking. Most antique towel rails show this kind of colour variation.