Awards are flexible so, yes, it's possible to change the dates...in theory. The stumbling block (on CPT you'll surely hit it, you did well to get 2 seats in the first place!) is you need availability in the award bucket on the new date too...

You'd need to call up BA and talk through this on the phone, it can't be done online (at least, my 2:1 reward booking had the change options greyed out).

Phil