In addition to my ongoing PbP, one of my gaming friends has asked me to run a Pendragon campaign for his youtube channel (which I'll be sure to link here somewhere), so we're in the works for setting characters up, and I've had a thought that it might be interesting to have the players start in 479 or 480 as household knights of Ellen's father Gwylon rather than Roderick's. This would allow them more of a chance to impress Uther in the first few years, guarding Ellen at court, give them a proper tour of the Kingdom travelling with the royal eyre, and give them perhaps a different angle of the Blains-Roderick feud. In the anarchy, they'll have technically been Ellen's men (though under Roderick's command) the entire time, so they might be in more of a unique position in her court.

Anyway, I'll probably have to make most of it up, but, any canon information about County Silchester, Sir Blains, or Levcomagus would be really very useful.

It doesn't sound that it would make a great big difference. As you say, the PKs would have more of an attachment to Ellen, which can help them in Anarchy. On the other hand, it probably closes some doors on seizing power for themselves, and in any case, by Anarchy they are likely the most glorious surviving knights anyway, so it is not going to be a huge difference: the countess would rely on their advice anyway.

The big difference can be the Blains-Roderick feud. I might be tempted to play up Blains as more of a charming suitor, who is paying more attention to Ellen herself, while Roderick is more about her lands. Just to have that dichotomy of 'who is the villain here, anyway?'. :P

As for information on Silchester, Blains and Levcomagus, The Marriage of Count Roderick is about as good as it gets on Blains, alongside with some information on Ulfius and his lands in BotW (and BoU). What is REALLY striking (and something I didn't notice until now) is that Ulfius has not that many lands in Silchester itself: only Levcomagus and Straightfield, both termed as manors, and Branch Abbey Hundred, adding up to less than £100. (And the Silchester castle, of course, but it has no income by itself.)

Blains probably has some other holdings held from Ulfius in addition to Levcomagus, to make him appear as more than a blip in everyone's radar: a mere vassal knight (even if a rich one) would not be an appropriate foil for Roderick or the PKs during Anarchy. Something like £100 in enfeoffed holdings from Ulfius (or some even from the King himself) would make Blains closer to a minor baron, explaining how he can afford small raiding parties of knights and so forth. Still, by himself he is not a threat to Salisbury. It takes Ulfius' muscle to back him up.

Interesting take. Morien has covered the bases so I cannot offer much except some of my own campaign take on Ellen's family. (Please note that while I've read as much of the material as I can, it's all a big soup in my head so I'm not prepared to offer citations at the moment. Apologies. :( )

<Khanwulf backstory, YPWV>
She had two older brothers, IIRC, and during Ambrosius' AD 468 "ransom and homage" lap around Logres the king stopped at her family's estate (which would have been about the closest approach to Saxon-held lands). These stops were effectively an opportunity for Ambrosius to assess the value of his kingdom and ransom nobles who surrendered at Caer Leon and needed to swear proper, public homage to him instead of the Vortigern. Fortunately her brothers got into the wine ahead of the planned feast and discovered it was poisoned before it could be distributed. Unfortunately they died, leaving Ellen as her father's heir. The incident was a huge embarrassment to the family, but they hanged some Saxons, blamed the Vortigern and Rowena (then besieged in Caer Vortigern), and the king forgave her father.

Her father served High King Ambrosius with great enthusiasm and well, gaining additional lands but unable to have further children with a wife passed that age. Eventually he was killed in battle--perhaps in 480 when the High King died.

Meanwhile, I've had Blains as the youngest son of a crop of seven, their father already Castalan of Levcomagus for the Vortigern--a role that continued under Ambrosius up until Uther ascended the throne and granted the land to Ulfius while creating him as Duke of Silchester. Keep in mind that Ulfius was one of Uther's closest boyhood friends and a constant companion and source of sage advice (and, "fixing" problems for him). Thus, Blains' family represents a long-term and glorious entity in southern Logres, a gem in Ulfius' crown, so to speak, and one to be rewarded with lands and accommodations to ensure his loyalty and that of his family. His brothers have gone on to hold manors in their own right, spreading the family around and representing in aggregate a force sufficient to sustain the long-term animosity between Blains and Roderick.

Hope this may help!

--Khanwulf

Blains and his (unnumbered) brothers are mentioned in 5.x editions, but in 4th edition, set in 531 AD, this is mentioned:
"Its steward holds a fierce grudge against all men of Salisbury because the old earl, father of Robert, slew all of the steward’s brothers in combat."

In 5.x edition the brothers are still alive and the feud predates their death.