Pearls that resemble my great grandmother's necklace. Please help identify.

[Ray91]

Hello knowledgeable pearl people. I have learned a lot since I found this website, so a huge thank you to everyone .
I'm hoping I get some advice regarding a necklace I have purchased some time ago when I visited my home country.
The necklace looked so much like my great grandmother's necklace except the pearl were smaller. My grandmother, who passed away long time ago, told me that her mother's necklace is very expensive and precious. (I don't have that necklace as some family members inherited it and split it into single strands)
When I saw the necklace in question, I immediately recognised it to be of the same type of pearls. It even have same clasp model but in silver (grandma's had an 18ct gold clasp)
I assume they are natural pearls but not sure of their origin. Also what really bothers me is when I took them to a local jeweller to be identified, the jeweller said they are mostly freshwater pearls except for the larger ones.
I want some advice as I'm planning to restring them, and although I can see some that look like cultured fwp, the majority seems natural to me. So should I just remove the obvious fw pearls?
Thank you

 

[Pearl Dreams]

They do look like freshwater pearls....

 

[jshepherd]

It might be natural. I have a similar-looking natural strand. Some pearls might be cultured, but I think it's worth having a lab take examine it.

 

[willameeena]

Is the clasp original or signed?

 

[Ray91]

Thank you for your replies everyone.
Some of the pearls definitely look like freshwater pearls, but in real life they stand out in the strand as they are really different to the rest which are more translucent and have silky lustre.
The clasp is not marked, not sure if it's original. It's exactly the same clasp model that grandma's necklace had, except that one was 18ct gold and was unmarked as well.
I am considering sending it to a lab, but I don't know how that works. Does the lab identify each pearl so I can separate the cultured and natural? or does it give a general statement it's a mixed necklace?

 

[Pearl Dreams]

GIA would identify the natural pearls, if any.