It would surprise me if people with that much money didn't have a state of the art security system. If it was murder, and I think it is more likely than murder-suicide, then perhaps the killers knew how to gain entry silently, and turn off the alarm system.
Warren Buffet even has full-time security guards around his home and office, I have read. I am even surprised that they did not have drivers who were also body-guards at the least, but apparently Barry liked to drive himself to work in an old car, and Honey finally bought him a new one. I wonder if she just drove herself around too ? If someone managed to get in his/ her car, and forced them, probably at gun point, to take them into the house by way of the large 6 car garage, next to the pool, that could explain not seeing anyone going into the house, if they hid in a back seat when approaching and entering the garage ( if there are outside security cameras ). It would also explain the lack of forced entry. Honey was out and about more than Barry it seems, and she would be an easier target. Maybe that is why she was killed first somewhere else in the house. She may have tried to warn Barry, and they silenced her. Then possibly they forced Barry to the pool area, killed him there, and brought Honey's body there as well, and staged it to look like a murder suicide. Just a theory. If it was murder, it was well planned ahead of time.
The house looks staged, and I doubt that they would have expensive jewelry etc. on the property when it was being shown by real estate agents. Was there a safe, and would thieves have perhaps been trying to force Barry to open it by partially strangling Honey, then things went terribly wrong -- they killed her by accident, and then had to kill Barry too, staging it to make it look like murder-suicide without ever making him open the safe ? Wild conjecture I know, but just trying to think of some possible logical explanations.
Did all the other robberies in the area happen only when the houses were not occupied ? Did security cameras gather any information, or were they disabled ? It seems that LE is having a hard time catching these thieves. IMO