Q:

How much HP/MP you get with Vampire/Siphon/Balance runes?

There are 3 types of runes in this game that will restore some of your HP, MP or both.
Vampire rune = Restores HP when enemy is killed
Siphon rune = Restores MP when enemy is killed
Balance rune = Restores both HP and MP when enemy is killed
Balance rune seems nice, but I'd guess it restores less then other runes.
How much HP/MP do each of this runes restore? Is the amount they restore fixed or is it based on your level or max HP (of either you or the enemy)?

A:

They are all fixed amounts:

Vampire rune = gives 2 hp for every kill
Siphon rune = gives 2 mp for every kill
Balance rune = gives 1 hp and 1 mp for kill (.5 Vampire and .5 Siphon)

and they do stack, with each other or themselves, with each one giving the same fixed amounts.

A:

Vampire rune = 2 + [heir+number]* HP per kill
Siphon rune = same effect as vampire, but for MP instead of HP.
Balance rune = Vampire and Siphon combined, but half the effect and rounded down.

for 9th new game, the values are (2+9)/2 = 5.5, rounded down so the value is 5 mana and health per kill.

Runes stack before they are rounded down. If you have 2 balance runes on 9th new game and nothing else in terms of vampirism, you'll get 11 HP and MP per kill (5.5 * 2 = 11).
* Heir+number is the number you see on your title screen. If your title screen is red, this number is 0. If it's green, but there's no number, it is 1. Otherwise you will see the number.

