This theory makes no sense though. Alex performed these murders alone.
If he "had it done," he would've been far away from Moselle at the time of the killings and had a solid alibi. The evidence clearly shows Maggie and Paul died at or near 8:50, and Alex left the property at 9:06. He did not "orchestrate" the killings. He is the killer. While it's clear he is not brilliant, he is also not stupid enough to hire a killer, yet stick around for the murders.
It's also not reasonable to imagine he had help. If he had someone help him kill them, he would've simply hired that person to kill them without his presence. And if someone helped him, that is one more person Alex has to hope keeps his mouth shut. It's simply unreasonable to believe anything other than Alex Murdaugh shot and killed Maggie and Paul by himself.