Right now, that’s just fan hype. That’s not confirmed yet. And even though we like them, half of them might get replaced.There will be plenty of new people (The La Forge sisters, Jack Crusher, Dr. Ohk, Mura, Esmar, [The] Shaw[logram]).
I believe this as before SNW aired, there were supporting characters introduced in DIS and Short Treks that were not carried over to SNW, despite expecting them to be involved with the show. Louvier was replaced by Hemmer, and the Pelia and Scotty in engineering. Amin was replaced by Ortegas and Jenna Mitchell at the helm. The comm officer Nicola was replaced by Uhura. Even Lynn Lucero, who - based on the Short Treks about her - had a history with Pike and has every reason to regularly visit the Enterprise crew after losing her ship, has been replaced by Kirk as the one who (annoyingly) drops by every few episodes. There was only a three year gap between DIS S2 and SNW airing.
If Legacy ever comes on, it will have been several years since PIC S3. In that time, Jack, Alandra, and Esmar will likely have ranked up to lieutenant. While Sidney and Mura will have ranked up to lieutenant commanders. Raffi might even be in line for her own command. I find it plausible that half of them (Mura, Ohk, Esmar) will have been reassigned to different ships in the time between PIC and Legacy, and we will be introduced to new characters.