No, Citadel does not own Melvin Capital. Melvin Capital received an investment from Citadel (the hedge fund, not the market maker) and Point72 this week.
> Robinhood seems to be manipulating the market to make it easier for Melvin Capital to cut their substantial losses.
Melvin already cut its losses this week, as was widely reported. There is no evidence for the counter claims that they're lying, which themselves originate on reddit. In particular: all the widely cited short interest figures on reddit which purport to show this are out of date (usually by weeks), and even if they were true, they would not be proof the short positions weren't closed.