Can I change the fabric on it?

Reupholstering an antique ottoman is standard practice. The fabric is meant to be replaced when it wears out. A good upholsterer will strip it back to the frame and check the springs. They can fit a fresh cover while keeping the original horsehair and shape intact.

My husband wants to use our big square one as a sort of table in the middle of the room, is it strong enough for that?

Most Victorian frames are built with substantial timbers to take the weight of several adults sitting down. Using one as a central table places far less stress on the joints than its original purpose did. You just need a solid tray to provide a flat surface for glasses. The deep buttoning makes loose items unstable.

How do you clean the wooden feet?

A soft cloth removes everyday dust. If the timber looks dull, apply a thin coat of good beeswax polish and leave it for ten minutes. Buff it off briskly with a clean duster. Avoid modern aerosol sprays because they build up a sticky residue on the finish over time.

I was wondering if the wheels on the bottom mean it was meant to be moved from room to room or just pushed around the same carpet?

Castors were designed to help servants slide heavy seating around a single room. Drawing room layouts changed depending on the time of day and who was visiting. Pushing them over thresholds or stone floors often damages the brass fittings. They roll best on the thick carpets they were originally made for.