How to locate imprisoned lord to rescue him

It seems that most polearms in the game do not support a swing attack while mounted. The only such pole arms that allow for 2 handed swings are the hafted blades and their variants. These are the same weapons that the Khergit lancers sometimes use, which is how I noticed their uniqueness.

The best way of getting a castle or town is to capture one yourself. Keep an eye out along the borders where towns and castles frequently change hands. Those places usually have a rather weak garrison so you should be able to take it without too much trouble.

When you capture a town or castle, you can make the request to your king that you want to keep it. Unless you've just recently been rewarded a fief, the King will almost always grant you the town/castle you've just captured. Don't count on the king giving you one otherwise unless your reputation with him and the other lords are all super high and you manage to convince them to support your cause.

If the castle near your village is already owned by a lord (almost 100% of the time it is), then you are out of luck, you can't get that one unless an enemy faction captures it and you retake it.