I trust the following should clarify the issues raised.
1) The unit of cavalry has chosen to enter the zone of control, and in doing so, attack both units of infantry. The cavalry unit can add any impact bonus entitlement because one of the two infantry units is in the open. The infantry can use the highest combat factor of the two, plus the total number of stands, which would be 8, presuming that the infantry are 2 units of 4 stands, plus any impact bonus for the infantry unit in the open.
Heavy cavalry B class: combat factor 5, impact bonus (+4) 4 stands. Total combat points = 13
Infantry unit 1 (in the woods) Militia c class: combat factor 2, 4 stands
Infantry unit 2 (in the open) Heavy infantry B class: combat factor 5, impact bonus (+1)
Total combat factor for both units = 5 (+1) + 8 = 14
Result after both sides roll 1D6 :
+3 to Heavy cavalry = B class infantry recoils 1 hex, C class Militia recoils 1 hex and becomes disrupted. The cavalry can choose to either follow-up the infantry in the open or follow the militia unit into the woodland hex. To follow-up the recoiling infantry unit in the open, would enable the cavalry to retain its impact bonus (+4), however, this would be lost if the cavalry unit decided to follow-up the militia into the woodland hex, and they would fight ‘as if disrupted’ by not being able to count their stands in the next Hand-to-hand combat phase.
+3 to the two infantry units = B class heavy cavalry recoil and lose impact bonus. Either of the two infantry then follows-up the recoiling cavalry and occupies the now vacant hex. The heavy infantry retains its (+1) impact bonus
In both of examples above if any of the recoiling units are unable to make a recoil move without entering the zone of control of an enemy unit they are removed from play.
2) Only friendly units not in hex-to-hex contact with an enemy unit i.e. not in the ZOC of any enemy units, can be pushed back one hex to make room for the recoiling unit. Any unit pushed back or displaced automatically becomes disrupted.
The issues which you have raised are clarified in the up-dated version of the Hordes & Heroes Medieval rules which we are preparing for release in early 2018 along with extended and revised army lists.