Lets go through them one by one.
Arien: Is one of the most powerful Maiar.
That would warrent either at least 6-B, or unkown. We are also completely ignoring her sun-moving feat. It should be stated that while she moves the sun, it is likely smaller than the real one.
Personally I think unknown is the best option.
Osse: Should be comprable to Arien and nearly as strong as Sauron.
Given how high-end 6-B (To the point of being Country level+), I think at least should be used here, especially when the Balrogs can perform far more impressive feats. Also, when was it stated he was comprable to Sauron, or Arien.
Tilion is reasonable, because, he was just a no-name servant of Orome before guiding the moon. He would probably be unknown, for the same reson as Arien.
Balrogs: Balrogs were described as some of the most dreadful servants of Morgoth, which included high-tier Maiar like Sauron. Seven Balrogs were able to drive away a starving Ungoliant, who overpowered a weakened Morgoth. All Balrogs are Maiar, and remain very powerful
First off, the most glaring issue, is that they drove off a full-power Ungoliant, not a starving one. That definetly warrents an at least 6-B rating.
Additionally, Sauron is at least 6-B, not plain 6-B.
This is the problems I've found so far.
However, I'm certain I've missed some, and probably have some kind of problem in my proposed power-scaling.