Photography for a registry office wedding

We are planning to have a very small wedding just my partner, me and our 3 kids (we are a blended family, she has 2 girls and I have 1). Planning to marry at the registry office in Kensington. Has anyone done this or similar and know what options are for photographers, it's not a all day wedding, just a quick ceremony. Do photographers cater for such a short time? Know they normally cover a few hours to a whole day, but we really only need them for a short time, to capture a few pictures from our ceremony.