Read over the subject form on the link below. It is self-explanatory. The person swearing under oath to the details on the affidavit must have personal knowledge, under penatlies of perjury, about all the information on the form.
There is not any limitation on who can complete the form and attest to the facts, but it does need to be someone with the personal knowledge to do so. The estate, however, will be distributed to those entitled to it as designated in the Small Estate Affidavit, not necessarily to the person making the affidavit. Also, as a practical matter, I expect many who consider acceptance of the affidavit may consider the risk too high if the affidavit is prepared/presented by someone without some sort of relationship to the situation. I would be pleased to consider this matter by initial telephone consultation.