I tried to match the shirtlessness and towelness icon (yes, those are words) with some of Barnabas' but let's face it. It's awkward.
ANYWAYS.
Caradoc would know him, as he's a mopey emo Order member and general douche. He's kind of a lost-child of sorts and would reluctantly listen to whatever Frank told him to do, as while he wouldn't want to admit it, but he'd look up to him. Of course, being the loser he is he'd mope and roll his eyes, but he'd secretly value what Frank thinks.
Geoffrey is usually busy with his DMLE business, Death Eater obligations, and filing away paperwork, but he'd keep an efficient eye on the Auror anyways. He probably makes nice on the outside as he always does. He's really quite dull.
And Barnabas just buzzes about and tries to find opportunities to rile people up, even if he's not at all successful. So nothing much established there, but he'll be around.