So, my understanding is that the main branching of history in Parallel time is that Barnabas doesn't fool around with Angelique in the 1790s, resulting in his happy marriage to Josette, their son Bramwell, and the differing generations that follow, yes?
That being said... does that mean that Brutus Collins, and the events surrounding him and Constance, Amanda, James Forsythe, and Sarah still happened, since the branch is apparently later with Barnabas and Josette? According to the wiki, Brutus was around from circa 1630 to circa 1680, and murdered a bunch of people and hid the bodies in the forbidden room in the West Wing of Collinwood. Which is a problem, because Collinwood didn't exist at the time. Hell, the Old House didn't exist at the time, either. And according to Big Finish, Isaac didn't even make his trip to America until 1690, ten years after his own death.
So how do we reconcile this.
Well, Blood & Fire actually gives us a nice answer to this conundrum.
What if the "New House", what is now know as Collinwood, was built upon the foundation/remains of Anchor House? Anchor House was the Collins family home until at least 1767, when construction of what would later be known as The Old House began. It must also have been the house that Isaac was staying in in The Crimson Pearl. If Collinwood was indeed built upon or out of Anchor House, it would explain why Isaac's ghost appeared in Collinwood in A Collinwood Christmas, rather than in The Old House. He was appearing in his own room, as did Jenny and Trask. It would be odd if he were the only ghost not to appear in a room associated with them.
So what if the Collinses had lived in the area for some time. It's said that Isaac started the fishing fleet and the town, but what if the town was just built up on lands the family already owned? Anchor House obviously precedes The Old House, so who's the say how long it's been there? Brutus and co could just have been the extant branch of the family living in the Americas prior to Isaac crossing with his wife and child. We know that Isaac's father Amadeus was a judge of some renown in New England, presumably he built up this reputation over a period of some time, so one could easily surmise that he was perhaps established in the area already when his son sailed over with his family.
I propose that Brutus was cousin or uncle to Amadeus, and was the head of the family in the "main" timeline during the middle 1600s as well, and that Constance, Amanda, James, and Sarah, and the events surrounding them, all happened as they were described in the Parallel 1841 storyline, but, in the main timeline, the events of 1795, with Barnabas being cursed by Angelique, and all the various deaths and events surrounding that, the lottery of the forbidden room was forgotten to time. Also, that the New House, known now as Collinwood, is built upon the old Anchor House from Blood & Fire, the Collins family home prior to the construction of The Old House.
It could be interesting for Big Finish to revive this plotline in the main timeline, having someone discover the room, and disturb the restless ghosts...
*quick edit: I'm seeing sources that say Amadeus was Isaac's brother, and other sources that say he was Isaac's father, and I can't be bothered to sort it out as it's tangential to my point about Brutus and Anchor House.