I'm not sure we would be that desperate for cover. I imagine we would rather start Webster at the back, and Trossard/March on the left. And with injuries we still have Van Hecke, Duffy, Clarke etc. No way are we getting Colwell on loan
I'm not sure Clarke or Duffy will be here by the end of the window, especially if we feel Colwell is better than both and he's offered as part of the deal. That could be buy, loan or loan to buy - we'd simply adjust the fee part of the fee plus player.
Losing Cucurella leaves a massive, massive, hole to be filled. The bloke can play left back, left centre back, left wing back and left midfield equally effectively - he's probably more versatile and just as attacking as Robertson. None of the players you've named can do all of that and using Trossard as a LWB would effectively commit us to blooding Mitoma in an attacking role.