Control have already been explained : the control points are for each minis, so if a unit of 10 minis with a control point value of 2 is on an objective, they worth 20 control points and you will need more than that to take the objective back.
Regarding rend, I don't see how it can change, we've seen that il will be way more difficult to stack +1 save as many iterations have gone so I guess it will be more difficult to reduce ennemi's rend but it will work the same as now otherwise