Both are weak. Vampire Pit is an overly nerfed Boneyard, with higher cost, costing to use ability, and only enemies, and the only benefit is that the creature is vampire, but... for that cost it sucks anyway.
Sirens call is basically... well, just see for yourself. Costs 5-8 Water, then you have to use 3 Water or Air JUST TO GET UP TO 5 EXTRA DAMAGE. WEEEEEEEEEEAK. and every second turn, to that.
Give them real buffs. Make the Vampirepit cost 8 Darkness, but generate Minor Vampires or free or 1 Darkness, on each death, and the Caller... knock off the attack limit and the "every second turn".