How to chown "www-data" and another user to the same folder?

i’m creating a web server with Debian9, where i want to have hundreds os sites.

Each one inside “/var/www/” Ex: /var/www/site1/ /var/www/site2/ /var/www/site3/

I make tests where i created a user “user1” and set permissions to “user1” write only to “/var/www/site1/”

when installing wordpress on the folder “site1” i have to chown “user1” to “site1” folder, so the “user1” can put and write all files needed using sftp protocol.

But when wordpress needs to write .htaccess file or create a new folder to install a new theme, i need to chown “www-data” to “site1” folder

My question is: Can i chown at same time “user1” and “www-data” users to “site1” folder?