The location?

Where is the fictional location?

In "Viking Funeral" Thorfin was apparently left behind and his crew sailed back to where they came from, which I think is described as "Canada".

That resumably means that the show happens in the USA.

The revolutionary War ghost Isaac despises Alexander Hamilton and so obviously met him when they were alive.

Hamilton fought in the battles around NYC in 1776 and in the Battles of Trenton and Princeton. Hamilton sepent 4 years as a staff officer for Washington and thus marching whereever Washington marched. Hamilton Commandthe US units which, alongside French units, captured British redoubts at Yorktown, thus forcing the surrender of Cornwallis.

So Isaac should have met Hamiliton somwhere that Hamilton went with Washington.
I believe Isaac supposedly lost Fort Ticonderoga in upstate New York, which was actually abandoned by order of Arthur St.Clair in 1777. And Isaac is said to have died of dysentry 2 weeks after that, so he must have died somewhere in the Northeast.

Samantha and Jay lived in New York City, and the estate is probably fairly close to There.

And Sasappis is said to be a Lenape. So depending on when and where he died, he might have died within Lenape territory or outside it.

I suspect that the fictional location is somewhere near the Hudson River, in the 120 miles or so between Fort Ticonderoga in the north and the northermost limit of Lenape territory in the south.