Do antiques sell for their market value? As in, how liquid are antiques?

My family has an estimated 1.1 million USD dollars' worth of heirlooms, paintings from dead chinese family artists in the line, and random acquisitions over the decades. However, I've had a LOT of arguments with my mother over the liquidity of antiques since she always seems to acquire things like John Gilbert Sterling Silver-Ivory dining sets (valued at >2k USD) for bargain prices in the hundred dollar ranges. I was wondering if anyone has had any experience with selling antiques? Is there a legitimate site out there where there are eager collectors to sell to?