Re-Employment during Redundancy Period

I would greatly appreciate advice and comment on the following please.
We have a team of 32 in a call centre. It is the type of industry where we have a naturally high turnover of staff. We have lost a contract and must make 12 positions redundant. All staff work on all contracts. We have selected the 12 by statistical performance measured by the call centre computer system so it is completely objective and qualitative. We have gone through the consultation period and the 12 affected staff are on notice ranging from 1 week to 5 weeks. Two staff will receive redundancy payments. We are near the end of week 1 of the notice period. Some staff will leave this week. Since giving notice to the 12 affected by redundancy 2 further staff have given notice that they wish to leave. Person A will leave at the end of week 1 of the notice period of the 12 being made redundant. Person B will leave at the end of week 2 of the notice period of the 12 being made redundant. There is very little opportunity to cover their positions with overtime offered to the remaining 18 staff. So we could be in the situation of recruiting for two positions whilst some of the affected 12 are still working their notice. Where do we stand on this issue please?
A further problem is that IF we can recruit for two positions whilst some affected staff are working notice then it would make (good economic and moral) sense to re-employ two of those made redundant. Reverting back to the selection for redundancy we have two particularly good people who are leaving us. Both of these two are on 1 week's notice and so due to leave at the end of this week. If we can re-employ them can we (legally and morally) re-employ them whilst a less good member of staff is working out their redundancy notice?
I would greatly appreciate advice and comments over this detailed and difficult situation. Thank you to any responders, in advance.
AdvicePlease

I expect this is coming too late, but if the staff are still employed, working their notice period, you don't need to reemploy anyone, you just need to keep them employed, so write withdrawing their notice and confirming that following a change in circumstances you are happy to keep them on.

To avoid claims from other staff you will need to ensure that you keep those with the next highest scores in the redundancy consultation, so you end up with the 10 who scored lowest being still redundant, if that makes sense.