How do I polish a brass fender?

Brasso and a soft cloth work fine for most pieces. Apply a thin coat and let it haze over before buffing it off. Fine wire wool helps lift stubborn marks. Go gently to avoid scratching the surface.

I have a wide fireplace in an old farmhouse and need to know if these can be cut down or altered to fit properly?

Cast iron cannot be resized easily. Cutting the metal destroys the structural integrity and ruins the moulded corners. Sheet brass models offer a bit more flexibility. A skilled metalworker can sometimes shorten the straight middle section and rivet it back together. It makes more sense to find one that fits. The trade produced antique fenders in endless sizes, so a close match usually turns up.

What are the side pieces called?

Dealers call those side sections the returns. They frame the hearth and angle back to the wall.

My husband bought one with leather seats on the ends, but the leather is torn. Do upholsterers fix this sort of metal furniture?

Traditional upholsterers handle club fenders all the time. The padded corner seats unscrew from the metal bases. They rebuild the horsehair stuffing and stretch new leather over the wooden seat boards. The metal frame stays untouched while the top pads get restored.