1) I'd give it one more "Captain, you MUST go around" after the initial go-around call. Whether I'd announce "I have control" would depend mostly on how he reacts. If he says nothing and just carries on, you would have to worry about incapacitation. If he just says something like "look, it'll be fine, I've been doing this for long enough", I'd let him carry on as long as it does not get too scary (i.e. you're half-way down the runway and he's still trying to land). Like Blackcoffee said , wrestling the controls should be left for a fairly desperate situation. I WOULD write a report though.
Don't know about your company, but mine uses FLIDRAS and captains are well aware that not going around at the gate (500ft) when outside the envelope will result in tea with no biscuits. Therefore ignoring a call for go-around tilts the scale strongly towards incapacitation.
2) Again, as long as it does not look like it's about to go out of control, I'd just write a report (and follow up on it). Wrestling is the last option.
P