I keep hearing that there are ~300 first-language speakers, but I can't find much evidence for that. There are a few people who only spoke to their kids in Coptic and therefore there are a few families who definitely speak it fluently, but I have no idea how to get in touch with those people, and I have no idea what their pronunciation is like. Probably Greco-Bohairic, if the people in this video are any testament: https://www.youtube.com/watch?v=qTjsZJNDLJw
Still, someone like that would be immensely helpful for grammar, etc.
I read somewhere too that there were some people who may have spoken Coptic through passing of their family. The sources are far and in between and I haven't found any more information on it.
Some of the aspects of pronunciation, phrases and Grammar do get passed from generation to generation, which is why, when I try to reconstruct middle Egyptian I not only use Coptic but also look at colloquial Egyptian Arabic. I understand there's a genetic indirect relationship there, and I say this because -
I'm Puerto Rican, and I grew up with Spanish, but if you know a little bit of the history of Puerto Rico, originally it was inhabited by the Taíno Indians whom the Spaniards (along with European diseases) killed off the people. But within the dialect of Puerto Rico, sounds, words and phrases got passed on through the Indians into the Spanish which is spoken on the island and indirectly, you're able to reconstruct some aspects of the Taíno language which is actually another one of my projects other than ancient Egyptian.
There are groups on the island and off who are trying to preserve the original mother tongue of the Taíno language.
The same process can be done with Egyptian.
Trying to get ahold of people from the countryside, away from the larger cities whose generation has stayed within Egypt is where you'll find some genuine answers, in my opinion. I'm surprised a group of people other than the Coptic cchurch haven't tried to preserve the original language.