Your troops should be able to hold against them, provided the knifers hold up, at least long enough for the other forces to get into position. However, if you kept the flankers to just knights, you could do a lot more damage, and have a much larger element of surprise. Troops marching on their flank would give the enemy commander a chance to pivot before his forces were engaged, though he's be in a much less advantageous position. The centre of the valley would become a killing ground, likely for both sides, but you have the numbers to overwhelm them. Also, if you did force a pivot, they would have a much harder time escaping, and would therefore be more likely to break.
In summary, troops marching likely means more casualties, but has good odds of producing a significant victor, possibly destroying the enemy force entirely. Knights on the flank would be safer (for the foot soldiers, not necessarily the knights), so fewer casualties, but the enemy would be more likely to escape.
That's the tactical analysis of the chosen overall tactic. There's also a standard battle array - it would be a quick fight, and you're pretty certain you could force the enemy to withdraw without much effort. If you get lucky, they could even break, but you casualties would be lower.
