Asking with genuine curiosity: Do you have a narrative that would account for the scene and both murders?
What has bothered me about this case from the start (other than the fact that it's unsolved) is that the murders took place in the family home. A confrontation that escalated or was miscalulated (e.g. the person intended to confront Barry but instead, Honey was home; they struggled; she was killed; then Barry arrived and he was killed) seems more plausible than planned homicide. It seems incredibly high risk to intentionally kill two people (directly, or by proxy) in their family home. It's physically demanding, the opportunities to leave evidence are many, and the timing had to be perfect. I'm sceptical this was planned.
My sole conviction about this case is that there was one killer. Ultimately, evidence is the only thing that matters.
The theory I have rolling around in my head is similar to yours, but opposite in some ways. I think the person went to the home to talk to Honey. After all, she was known to be the driving force behind the new spending that was going on. Barry told everyone who would listen that he did not want to move; Honey was insisting. The mansion was going to cost many millions, and meanwhile Barry was calling loans of far smaller amounts. To a desperate person, this might have seemed petty, a problem that could be resolved.
He may have hoped to convince her to get Barry to stop pursuing repayment. He may have intended to threaten or harm her. He may even have imagined that if she died, Barry would return to his usual generosity. Regardless of his intentions, the situation escalated.
I think the person did not have detailed knowledge of the Shermans’ changing schedules and had expected Honey to be home alone for hours that Wednesday evening. But that was an unusual day. She had a late-afternoon meeting and then went shopping. She arrived home much later than usual, and by then the perpetrator may have been waiting for hours and not have realized how little time was available. After all, the conventional wisdom was that Barry “worked late” every night. The perpetrator may not have realized this meant he left the office around 8pm and continued to send emails from his home. Barry got home about an hour after Honey did.
I think the perpetrator found himself in a situation where he felt there was no return. This is further into the realm of speculation: he may have had Honey’s body in position, ineptly staged as a suicide, and been interrupted when Barry came home. The underground garage is just on the other side of the pool; his headlights would have been visible through the glass wall. At that point the killer might have improvised. He was already a murderer and his options were to get caught red-handed or kill the person who happened onto the scene.
This would explain why Honey has injuries from a scuffle, and why Barry has blood on his pants, possibly from being lifted over her. Her body was already in place and the killer had expected to get away unnoticed rather than committing a second murder.
One problem with this theory is that it requires the killer to be very familiar with or at least confident around the Shermans, moving about the house and showing up for a conversation. Yet the Sherman family and friends do not recognize the walking man. Barry had a wide and oddball circle of friends. Maybe the perpetrator wasn’t an “inner circle” type. Or maybe he’s in disguise; if that’s the case, it strongly suggests he intended to murder Honey, not just speak to her.
There is no evidence of a second person so I believe the walking man acted alone.