The problem won't be ability but the routines they end up with.
Danniella's done a great job with the last two characters she's had, but they've contained no skating. If she ends up with a routine that allows her to combine the two then it'll be fine.
Hayley needs a 'wow' routine to bounce back from the slightly insipid performance this week (which was entirely the fault of the routine's style - she did as much as could be expected with it). However, 'wow' routines this week will need 'wow' solo spots, so she'll have to master whatever she wants to include...
Gary would be best off with a routine like Hayley's this week - one where the character is a bit less 'out there'. The solo stuff will hold no fears for him, it's just the rest of the performance he'll have to worry about.
I think Kieron's probably overdue a proper romantic slushy number as well, which could be a bit more challenging for him than the 'out there' stuff - although he's risen to every challenge so far and I won't expect any less of him this week. I do worry that his leg lines aren't very good compared to the others though - it might show when he's on his own, depending on what he's given to do...
Too many variables at present, but Mystic LL's crystal ball says that whatever lets these four down on the night, it's unlikely to be their ability to skate alone.