Some powers of attorney and other documents need a notary to witness the document plus two additional witnesses.
I have seen these documents more than once. Usually the client doesn’t inform me and then I have to quickly find two colleagues to witness the signatures.
If your document requires you to have these two additional witnesses be sure to raise this with the notary when making a booking.
Some notaries will charge for bringing in the additional witnesses. Some may not. You always have the option of bringing two of your friends (but note NOT family).
This way you are supplying the witnesses and there should be no need for any additional charges.
If you are not bringing the additional witnesses you should give the notary adequate notice so that he or she can organise for the two additional people to be available at your appointment time.