Trusting Cleophas I can excuse too. Even when Luke´s family clearly isn´t great since they disowned him because he became a werewolf, but I guess that´s just the "normal" amount of racism and blood purity stuff with Shadowhunters.
I feel soo bad for Izzy! And no she is not turning. She is just getting addicted. Back when we introduced vampires Jace explained that the bite (and by extension the venom) makes you feel kinda high. That´s why Simon was pretty happy being with Camille when she was biting him, and that´s why Izzy is so into getting more of the stuff from Victor.
And he absolutely must know what he is doing, he said he was a medic previously, he definitely knows Yin-Fen is not healing her and instead just making her addicted. And clearly he uses this to have a "spy". God he sucks so much.
I definitely took Alec´s reaction as him just being self-conscious too. But I´m glad they resolved that within the same episode and didn´t drag this out and make it a "problem".