Each Side's respective Doctor Who companion from the new episode
Roman - Rose Tyler
Patton - Clara Oswin Oswald
Virgil - Donna Noble
Janus - Ruby Sunday
Thomas - Rory Williams/Pond
Theorizing about the choices, both in the context of Logan being the Doctor and out of that context, below the cut.
Roman as Rose: For starters, the names sound pretty similar, both starting with ro. Passionate and loud, with a rather "opposites attract" dynamic with the Doctor/Logan. (I'm thinking specifically of Nine and Rose for this)
Patton as Clara: The heart of their respective duo (a bit more literally in Patton's case), who seems a bit shallow at first but overtime we see more and more of their depth. They balance out the Doctor/Logan well, and when they work together their joint perspectives typically bring light to the issue at hand, giving them the chance to save the day once more. (Like Sherlock and Watson, perhaps.)
Virgil as Donna: Snarky but well meaning characters with a heart of gold that they hide behind a wall of self worth issues and sarcasm. They have a pretty friendly relationship with the Doctor/Logan, although not without plenty of jabs, understanding each other more than expected more often than not, but still butting heads often enough for their stubbornness to cause problems.
Janus as Ruby: I'm sorry, I haven't gotten to 15s seasons yet 😭
Thomas as Rory: In season 5 to halfway through season 7, we see a lot of the ups and downs of Amy and Rory's relationship, and while it's never really the main focus it's an underlying theme of their seasons. Rory is a loyal, loving man who very much so adores Amy, but even with that there's still bumps in the road. In an episode about Thomas and the Sides worrying about how messy romance can be, this seems a very fitting choice. Also, looking at Rory's dynamic with the Doctor, Rory knows the Doctor is a brilliant man, but also knows that listening to him too much and becoming like him is one of the most dangerous things a person could do. I'm uh. I'm sure that means nothing in this context though.
And last but not least among the light sides - Modesty!Remus! He's very shy, maybe even too much, and self-inverted. It's so good that loving elder brother always keeps an eye on him :)