different numbers - one backup account only

Goodmorning everyone,
I have a particular need but not too much.
I use WZ in an Association and I have created a single Google account to install it from the PlayStore and use the same account for all mobile phones to back up Watzapp.
The question is this: Are the backups merged and mixed or do they remain "separated" on each physical mobile number despite having the same account?

Thanks if anyone has any useful information. I have asked the support several times but they answer with pre-packaged questions NOT useful for the solution of the problem