I was quite outmatched - though the Faction Leader's army was comparatively weak, the Faction Heir's army was full strength, with no less than 2 Elephants and 2 Elephant artillery units. The map was also very open, giving them a wide field of fire. Luckily, they were reinforcements, so I had time.
I dealt with the Leader's army without too much trouble, and killed the Leader as he tried to make his escape. However, by that time the Heir's army was within range, and I took an unholy beating from his elephants - it was clear that I had no chance of winning. However, the Heir foolishly left himself exposed, so I charged him with my 2x General's Bodyguards (Father and Son team) and killed him before ordering all units to abandon the field before we were totally crushed.
I lost most of that army (they retreated to Kiev) but the Timurids were destroyed as a faction and their two other leaderless armies with full stack elephants etc becamse small 4x horse archer only units. Sweet

However- it's not something I needed to do, so I loaded the game - time was on my side, not theirs. I can kill them next time they try and besiege a city.