The midfield duo have been out since pre-season with hamstring injuries.
They are working their way back to fitness and are not yet ready to return to action.
Head coach Mike Williamson, though, says the duo are making good progress ahead of expected autumn comebacks.
“They’re getting drip-fed back into training, but they’re not quite there yet,” said the Blues boss.
“I think it’ll be a week or two before they’re in full training, and then they’ve got to get match fit.
“They’ve obviously been out for a period of time each, so they’re getting closer, they’re working hard.
“They’re so honest and desperate to come in and affect the team, so they’ll be welcome back when they are fit.”
United have been depleted by injuries since the start of the campaign with midfield a particular area hit by absentees.
Along with home-grown Charters and summer signing Robson, the Blues are now without Dylan McGeouch for “a few weeks” because of a calf problem.
Harrison Neal impressed in his cameo on Tuesday night (Image: Ben Holmes)
Long-term ACL victim Callum Guy, out since last November, is continuing to make progress as he builds up his fitness ahead of a playing return.
Others on the sidelines include strikers Georgie Kelly and Daniel Adu-Adjei and defenders Ben Williams and Aaron Hayden.
Williamson said the “bare bones” nature of the squad was behind his decision to drop captain Charlie Wyke to the bench for Tuesday’s home defeat to Notts County.
The striker will be hoping for a recall to the XI at Colchester United this weekend as Carlisle seek to bounce back from their successive home defeats. Midfielder Harrison Neal, who impressed in a substitute cameo, will also be pushing for a call-up.
One plus on the fitness front has been the return of Jack Robinson. The defender was among the substitutes on Tuesday night having come back from an ankle injury.
