Hi, I'm so sorry to hear you were not yet approved, but you will get there eventually, dont worry! I would send multiple bank statements that cover the entire length of the time you've had the account in both your names. You dont have to print out every months statement, you can space them out 3 months (that's what I did at least) each.
We also did not own a home together or have any children at the time of applying for removal of conditions. I think I sent insurance, bank statements, proof that we had each other as beneficiaries on life insurance, plane tickets of travels taken together, photos, joint ownership of car, and other bills in our names.
Are you sure about your mortgage rate going up if you are added on the house? I feel like that can't be true, but I'm no expert. I would just double check that.