If the simplest answer is commonly the correct answer, and people murder mostly for love, money or jealousy, then I post a simple ( based on the minds of the known perps so far) theory that does NOT involve MS:
WW knows the nature of the office business. Bluntly, cash is collected, sometimes large amount of cash, and kept in safes in the home, not always deposited, for periods of time, maybe indefinitely.
WW is desperate for cash. And involves the other perp for a robbery. And if he is regularly driving to Florida, then this trip is no big deal. They are discovered by TS!
TS will NOT give up the safe combinations and codes, because she fears for her life, and knows that guns and ammo may also be discovered and used on her. If she is as feisty and cunning as everyone has said, she will try to make a break for it and leave the house. Maybe made it to the garage before being whacked? Or initially hit in the garage and dragged inside?
WW did not want TS dead, but the hired perp is of a low intelligence and emotional development and things escalate.
how much is a lot of money? To the perps? $10,000 cash?? $30,000 cash? Who knows. More than they have and more than they possibly need for the immediate future. Would also explain the "raise" the perp referred to. Would explain the rage associated with the killing: I came all this way and I Have nothing. Well I am going to get something! And it is you. And I am mad. I wanted the money. I needed the money. My girlfriend is pregnant. This trip has cost me. It is going to cost you.
hence the murder 2 charge for both, vs a murder one charge. Robbery as the intent. Murder as the outcome. No MS in the plan. Just my current theory, which rolls along every day, and changing with each moment.