Hrewsahgs:
+ K2 Strongest resistance, destroying both F1 and the ladder at the same time. The solver can play K1 to threaten F1 again, which the opponent will respond to. However, the ladder's no longer clean, just a ko.

Sadaharu:
H15 first instead of F16 connect should work too

jhubert:
When White plays atari at H13, Black can play J17, J18,J16, G18 and B18 wins the semeai. Correct solution is to play directly on J17