One word: Privateering.
Both those orders are mercenary types, so attacking the ships of whichever factions they haven't allied with is easily roleplayed.
That's a fair point. Though I do like the idea of the character having some stronger ties with the organization itself - maybe even being born into it (Deadfire culture). I could still make Goldpact work pretty well with that - there was a pretty rigorously upheld code of ethics aboard pirate ships regarding fair shares for fair work.
A good way to look at it! It fits very well with the Goldpact Knights' stance on payment being a binding contract. If the Prinicipi are paying them more than the RDC or VTC, then the Principi is who they will side with.
Keep in mind that Watcher has spent years away from his/her paladin order, so the code of conduct may have became quite flexible for him/her. So there is no reason why Bleak Walker or Goldpact could not decide to support Principi out of simple sympathy for their cause, even when there is no contract from them strictly speaking. It would not go against any of their dispositions.
Precisely. As I said, the conviction that grants Goldpact Knights their paladin powers is that payment is a binding contract, that personal sympathies and stuff shouldn't cloud the basic issue of who is paying you for what. For the Bleak Walkers, they gain their powers from their belief in total war. Even if they aren't being paid (but they often are), nothing less than completely crushing whoever their pointed at is acceptable, so even if the Bleak Walker Watcher doesn't necessarily give two hoots about the Principi's internal and external conflicts, if the Principi have hired them, the piracy is merely an opportunity to display the notorious brutality their order is known for. That said, Bleak Walkers also work because they're kinda ****, so robbing and murdering on the high seas probably would sound appealing to them, Principi or no Principi.