What happens if I save Berthold and his sister

Dishonored has two different endings depending on how you play the game. If you kill everyone you will get the evil ending (high chaos ending). If you don't kill very many people, you will get the good ending (low chaos ending):

• At the good ending you'll save Empress Emily Kaldwin.
• At the evil ending Corvo Attano dies.
• In the high chaos you can still save Emily

You can save Emily at the high chaos ending even if Havelock sees you, by stopping time and using blink to get directly in front of him.

You cannot see an exact value of your current chaos, but here are some tips:

• Weepers count towards your detection value if seen. They also raise the Chaos Rating if killed
• Rewiring traps that result in kills will count towards kill amounts and Chaos level
• Friendly characters do not count towards detection. This includes Rats, Hagfish, River Krust etc. They also do not raise the Chaos Rating when killed. This changes if they see you make a hostile/aggressive action.
• Wolfhounds do not count towards Chaos Rating when killed, however they can discover you and other bodies you leave behind. Best to kill these while hidden
• Killing under 20% of the characters in each mission should ensure the Low Chaos Rating score at the end of each level.
• Chaos Rating can have many effects on each level, such as increased enemy presence or different available items.

Blink-jumping is the term used to describe combining the jump (standard or enhanced with Athletics) with the Blink power.

You do it in the dream where the Outsider first gives Corvo his powers. In that dream, there are a few of the platforms that are out of reach of a normal blink; you have to trigger Blink, then jump, and release blink.

This gives you (a) a farther range than you have with Blink alone, and (b) the ability to move higher than you normally are able. As you increase your agility power, you are also able to jump further, and indeed to double-jump. Both of these predictably increase your mobility with Blink. With Blink 2 and Athletics 1, it is quite amazing the freedom that using these together effectively can give Corvo in terms of mobility.

In the linked question, note that the answerer says "I don't really see how better jumping can help someone playing a stealthy non-killing character...". I infer that this is the reason for the reference to Blink-jumping.