Gondor's Kin-Strife: Did anyone else take sides?

[Valandil]

Gondor's Kin-strife of the 15th Century, Third Age, had its origins in the mid-13th Century (TA) marriage of an eventual heir to Gondor's throne with a princess from an outlying tribe. Their "half-breed" son, Eldacar, came to the throne of Gondor at the death of his father Valacar in 1432. Open rebellion had begun in the southern parts of Gondor even at the end of Valacar's reign, and Civil War began immediately at the succession - led by Eldacar's second cousin, Castamir - who was Captain of the Ships and had his stronghold at Pelargir.

Castamir's forces moved northward and beseiged Osgiliath, finally taking it - and burning it - five years later in 1437. Eldacar fled, but his eldest son was taken and executed. The Tower of Osgiliath was destroyed in the fire (it was on the Bridge of Osgiliath) and the chief palantir of the South fell into Anduin.

Ten years later, in 1447, Eldacar had gathered an army of northern folk of Gondor as well as Northmen of Rhovanion (his mother's people) and drove southward, retaking Osgiliath, for the people had grown weary of Castamir. Eldacar slew Castamir himself at the Crossings of Erui, and pursued his army to Pelargir, but could not take the city. The following year, Castamir's sons sailed with their remaining forces from Pelargir to Umbar.

In this time, I wonder, what did the other kingdoms and peoples of Middle Earth do? Did some side with or support one claimant or the other? Or did they all just leave it for Gondor to work out? Here are some who come to mind:

• Arnor/Arthedain - King Araphor had come to the throne at a very young age (18) in disastrous times (1409), and was only in his early 40's when the Kin-strife began, and mid-50's when it ended - still very, very young for a Dunedain king. Would he have a preference for one king in Gondor or another? Arthedain was Gondor's sister kingdom - would it matter to them?
• The Dwarves of Moria were closer than Arthedain - but did they even have many dealings with Gondor?
• The Elves of Lorien, and Rivendell, and even Lindon - would they have preferred one over the other? Or thought of one as a more "rightful" king? Are they more likely to be sensitive to the importance of a pure Numenorean line among the Kings of Men? Or did they not think the distinction worth mention, much less fighting over? Or... would they rather just sing a song about something that happened a long, long time ago?
• What about the Elves of Edhellond? They were more in the thick of things?
• In fact - the ancestors of the Princes of Dol Amroth (already princes, as this was an appointment by Elendil) were right there in Gondor. Did they join in with Castamir's rebels?
• And then, the Istari. I suppose the infighting must have been grievous to them - especially Gandalf, I think. They had already seen the division of Arnor, and the resultant wars among those sister kingdoms. Especially if any (Saruman) were dwelling in Gondor at the time - what would they have done? Could they have stayed out of it, if they desired to do so?