Alex Murdaugh is a hunter. Unless he is the joke of all the hunters, he could have dropped them both with one shot each. And he could have shot them from 100 yards away with one shot each. He didn't have to be within feet of them or walk over for a kill shot to Maggi's head. No need for an up close and personal ambush.
Seriously, this is amateur shooting and the second shot to Paul being at such an angle is because the shooter fell down from the kick because he/she had no experience with shotguns. Paul heard his mom getting shot and tried to make it to her and shooter, splayed on ground, blasts again.
The second shooter had Maggi, but was not a great shot either. In fact, a truly poor shot. Shooting low, not experienced in shooting moving game. Unlike Alex.
Who kills the family of those who owe them money? Cartels.
Long guns disappear how? Stolen. Traded. Given.
JMHO but this is the scenario Eddie creates. Reasonable doubt.