But is it correct to say "It's more than we can do to do sth" as in Well, your offer is a little unreasonable, and it's more than we can do to accept it."
Yes it is correct.
"It's more than we can do to accept it." = "To accept it is more than we can do."
Or is it correct just simply say "Your offer is a little unreasonable and it's more than we can accept."
No, that's not correct. This doesn't mean the same thing. The offer seems actually to be less than you can accept. (Or the terms of the offer, or the conditions, or something else, are less advantageous to you than you can accept).
Compare something more concrete:
"It's more than we can do to meet you in Shanghai" Correct. (We can't meet you in Shanghai)
"It's more than we can meet you in Shanghai." Wrong. (Meaningless)
If my listed version above is incorrect in grammar or meaning please advise. In addition, how, in business situation, should I write emails when such meaning is needed to be expressed——The reason why I ask this is that I don't want to use I can't/We can't everywhere in an email or conversation. Hopefully you can help me with this. Thanks! Or if you have any other goods advice please kindly tell me as well..
Student or Learner