It is possible to win, but in an "unnice(I would say unKAM) way"
You have first to focus on bottom, set your horses and swordmen a little bit back, so they don´t get shot from the xbows. At the same time you have to jump to the north and let your warriors and your xbows do the job.
After a few seconds middle is attacked also. Now the unbeauty thing begins. You have really to fall back (where you started from). you have to take a good position with your xbows and split up the swordmen in a few groups (Some players even used the 1soldier-trick here, but it´s possible without). Now you have "just" try to stay on your side and let everyone in. After the middle attack is finished, you have to take a few swordmen and clean up the middle from the xbows.
Top should be finished now, bring the soldiers to the middle, to help there. Now you shall NOT go out, but still "camp" on your startingposition. At the same time the xbows from top, should stay also in middle, but watching from north on the battlefield. Now every wave should be killed once by once. Sometimes xbows are shooting to your xbows at the bottom, so you just have to show a bit xbowmicro(shoot and go back, before your xbows get shot).
That´s all
That is the reason I call this "unbeauty", because that isn´t a typicaly KaM fighting mission, where you have much possibilites to position your troops, to flank or to attack anything from behind. It´s a (for me boring) camping and "let them come" mission. If you are still not able to win it, I will post maybe a replay of it later.
If you want to play test certai missions, use the cheatcodes (Press V) or you can also do it that way: Press F11, Press Load , Go to campaigns folder, Open any missions like you want. (For example the last one, so you haven´t to play all missions before that one)