i would suggest write a letter as a cover page with all the additional proofs print and date and sign by both Sponsor and PA,
i think the police certificate is a separate upload and that would ofcourse be for the PA, again you can put a cover letter and explain who the PCC is for print date and sign by PA and upload as pdf files
so the uploads would be the following if there are 2 different upload areas
cover letter + proofs as one PDF
cover letter + pcc as one pdf
see what other members have to say as well, but thats what I would do