Hi Alison
My partner and I took my sister and elderly father about four years ago. I am sorry to say that it was dreadful. We only went for a day trip and the queue to get near the coach parking place was miles long. We arrived about lunchtime and went for something to eat straight away which was just as well as everywhere became so full that there were queues outside each eating place.
We have been to Lincoln for a long weekend before and loved the city.
However, at Christmas, because the streets are so narrow and steep, everyone is made to use them as a one-way system and there are wardens around to make sure that you don't go the wrong way. The streets were so packed that you couldn't get from one side of the street to the other to look in the shop windows.
The market itself is in the Castle grounds and is OK but not brilliant.
Having said all that, this was four years ago and things may have changed but it's not a trip I would repeat to check out.
Sorry to put a damper on your idea, but from my experience it is not a trip I would recommend. If you are staying for a long weekend it may be as well to visit everywhere very early before all the day trippers arrive.