Student or Learner
There are two sentences using very similar structures:
1. The two of them sat there chatting as naturally and easily as could be.
2. Each year before the New year, our family is as busy as it can be.
My question is: Are the two expressions (as ...as can be and as ... as it can be) of the same meaning? If not, how should I interprete the first sentence?
"as ... as can/could be" means "as ... as possible". In the first sentence, it means that they were chatting as naturally as two people could possibly sit chatting.
In the second sentence, your family is only as busy as your family could possibly be - not "as busy as could be", which might be a lot busier if you have a lazy family. This is not an idiom.
Note that your first sentence uses "could". If you're asking about a difference it's best to include only one variable. In this case, we'll assume that there's no difference between "as can be" and "as could be".