Yes, as long as you have at least 2 other sources between you apart from the HMRC letters, then that should be fine.
You will need 12 items, but only 3 different sources in total.
As you will be submitting individual documents, you'll need to get them as close together as possible.., for example, one in each name dated in January, one in each name dated in April, and so on.
Sent from my iPod using Tapatalk