There was no life insurance on Maggie or Paul (per testimony from the conservator appointed to manage his assets). The life insurance he mentioned in relation to that bizarre roadside incident was a policy on his life.
As far as I can tell, there was no reason for Alex to have logically thought at the time that the deaths of Maggie or Paul would directly resolve or assist him with the fallout from his financial crimes and wrongdoings. That doesn't mean the pressure from their imminent discovery didn't lead him to "snap" or that he could have mistakenly believed the deaths would help him, but I see no basis to say a person would logically think these deaths would be of any benefit to him.
Obviously, people commit murder all the time with a logically sound motive to do so (if such a thing exist), so even if you accept what I'm saying it has limited value in determine guilt or innocence.