Certified True Copy

Good Morning,
How does "Certified copy of your passport's bio-data page" work? I need to have 2 non-Australian passports certified for an Australian Visa and I spoke to the local Australian consulate who confirmed that they do have this service, but I couldn't figure out if this service is only for Australians, and for docs that are issued by Australian Authorities or for any documents issued by other overseas governments.

Let's say, I need to have a British and an Indian Passport Certified and I also need to have my
child's HK's Birth Certificate Certified? Would I have to approach 3 different bureaus to obtain true certification on these 3 docs?:

1)British Consulate
2) Indian Consulate and
then thirdly, I don't even know who I will approach for having the Birth Certificate certified as True, in Hong Kong, since the Home Affairs Department's website says it doesn't do certifications, just does signature witnessing. Any ideas on this too?

I believe that the Australian Consulate should be able to certify all 3, since the alternatives being the notaries or registered immigrations Agents, they also won't check the authenticity of any of these docs, but will merely confirm that the copy they have is certified as true of the original that I presented to them?

I am told that these docs should be certified either by:
a person who is the equivalent of a Justice of the Peace or Commissioner for Declarations (HK's in that place (for example a public notary); or a registered migration agent (whose registration is
not suspended or subject to a caution).

Reading past posts here, it seems rather expensive to have just few pages of docs certified by a notary public and I am not sure how much immigration agents charge, since don't know any.

Thanks for any help / input you can provide.