It’s been a while since I’ve worked with PDF-A validation, so I’d have to re-learn some of this stuff. Regarding the errors, you’ll just have to take them one at a time and brush up not he PDF-A spec. For example, When you save your TIFF scans and convert them to PDF you can use JPEG compression or Zip, compression, but not LZW.
It also looks like you might have some transparent and layered content in there, which isn’t allowed. Does that sound possible, maybe from a stitched or retouched file? If so, you’ll have to flatten those files before saving the PDF.