How to clean ormolu mounts?

Leave them alone if you can. The original gilding is very thin and rubbing it with modern brass polish will strip the gold right off. If they are just dusty, use a soft bristle brush. You can wipe them with a damp cloth if grime has built up, but dry them straight away.

My grandmother left me a large commode with a marble top that has a crack right across the middle, can this be fixed?

Marble restorers can repair cracks by pinning the pieces together and filling the joint with coloured resin. They match the original veining so the repair blends in. It isn't worth replacing the entire top. Original marble has wear patterns and edge profiles that are hard to replicate. A well-repaired crack is just part of the history.

What does commode actually mean?

The word comes from the French for convenient. It refers to the practicality of having drawers at waist height. English speakers later applied the word to nightstands holding chamber pots, which causes some modern confusion.

I was looking at one in a shop and the drawers felt very sticky and hard to pull out, is there a way to make them run smoother without ruining it?

Wooden drawer runners wear down over centuries of use. The sliding surfaces dry out and grind against each other. You can rub a block of solid beeswax or a plain wax candle along the bottom edges of the drawer sides. If the runners are heavily worn away, a restorer can glue thin strips of new timber along the worn track. This builds the drawer back up to the correct height and stops it scraping against the frame.