Um... since I think they're all offshoots from the PCUSA, which was formed by the merge of two other denominations, I'd say they're all equally 'related'. The PCA and OPC are probably closest in terms of doctrine and government.
When was the merger, about? It sounds like this was a bit later than the period I'm familiar with. The paper I wrote touched on the influence in the US in the late 18th century of the controversy over the Scotch Independency movement--here's a little info:
Presbyterianism Established, Meeting Of The Westminster Assembly
Nevertheless, amid all this apparent prevalence of Presbyterianism, there was a stubborn tradition in England of another set of antiprelatic views, long stigmatized by the nickname of Brownism, but known latterly as Independency or Congregationalism.
I was wondering if maybe that played a role in any of the divisions you mentioned, but it sounds like maybe that was a little earlier than you're talking about.