Not intentional on Valka’s part, she is kidnapped by dragons, and leaves Hiccup to grow up without a mother figure (there is no resentment between them and they love eachother dearly upon reunion)
yes, there aren't any deaths on-screen or blood but there's a scene where you can hear one dying off-screen which then shows its dead body + MANY mentions of dragons dying
No, but there's a scene where a few of the main characters should be forced to jump into the ocean tied up. But they free themselves and nothing happens. The scene is about 10sec long
Not a finger but several vikings wear a prothesis, for example Hiccup misses his left leg, Gobber a leg and a hand and Drago misses his left arm (but it's only shown 2 times in the movie for a few seconds).
There are two identical twins, one is a boy and one is a girl, and they're frequently mistaken for each other and people have trouble telling them apart and which one is the boy and which is the girl. This is played for laughs, and is a common situation in real life with identical twins.