When you tackle someone, I was treating that as an attack against the person your are tackling. It’s just rather than punching someone, you’re jumping down and trying to konk them on the noggin on the way down. So here you could have a more wimpy character might have a better chance of hurting someone if they get the drop on them so to speak. Now that you mention it though, maybe the jumper should take damage too?
For the ladder rules, it’s really just to make it easier to place your models someplace where they won’t fall off and break. So, if your movement would only let you move half way up a ladder, you can choose to either not climb it, or move to the very top and end your turn there
And yes in that case your target number will get +2 instead of +1, if you killed someone and then also had to change targets
And for damage you only ever take 1
HP worth of damage no matter how many saves you missed. In the old, old rules it was lose 1
HP per missed
D6, and people died way too fast