So, Persephone would know Dylan from all that eating of death that they both do. Alice may know him from various pureblood things. He's a lot older than both my guys, BUT, Dylan works with Guy's dad, Walter Dobbs, who is also an Obliviator, so there's that (his brother, Edward Dobbs, also works in the dept., Accidental Magic Reversal Squad, so Dylan may know him, too). I doubt Dylan would know Doyle or Marly. Well .. possibly vaguely know Marly from both working at the Ministry? Though they're in different departments and all.
Meredith, however, was only a year behind Marly and in the same house, so I'd be willing to bet they know each other. Plus, random connection, Mere's older brother's BFF is Marly's cousin, so ... yeah. It's possible they know each other through Boyd and Ed? Alice and Persephone would probably know Mere through purebloodedness, though Seph finds Mere's love of muggle things to be disgusting. My guys wouldn't really know her, but Guy would most definitely hit on her, and Doyle might try to filch some money from her and sell her counterfeit goods.