It is unfortunate that you are not getting cooperation from the institution from which you are acquiring the branch, but you actually do not need a lot of help here.
Under section 1003.3(c)(6) of Regulation C, the loans you are getting as part of the acquisition of the branch are reported by the institution that originated them. Your bank -- the acquiring bank -- does not report them at all. Check out section 1003.3(c) and the applicable official interpretations at https://www.bankersonline.com/regulations/12-1003-003#c.
What you will report are any loans for which the applications originated with the branch being acquired and were still in the "pipeline" on the date of the acquisition of the branch. Your bank will report on any of those loans made by your bank (and applications that are withdrawn or denied) after your acquisition date for the branch.
The institution from which the branch is being purchased is required to include on its LAR filing all loans originated through that branch prior to the transfer of the branch to your bank, as well as any applications denied, withdrawn, etc., prior to the transfer date.