Mens rea of murder is intention to cause death or GBH. Assess if Mo has this in relation to each person. Note in particular the notion of oblique intent in relation to Pablo.
The fact that Mo has PTSD & Depression is a big hint towards a few - I'd look towards the rules of Diminished Responsibility as a possible downgrade from murder, or loss of Self-control as you already identified.
You could consider Insanity, but I'm doubtful of it's success.
If a partial defence applies then murder will be "downgraded" to manslaughter.
If a full defence is applicable then there is no liability.
You can't really answer one without the other.