Connect a Block to multiple tables

I have a situation where I am using a form Block to add a user to a project. My database is in SQL Server. I want to connect One Block to multiple tables. Here is my scenario:

In my form, I have a user dropdown list that should look up the users from the Users table. I also have a project dropdown list that should look up the projects from the Projects table. Once the form is submitted, it should populate the selected user and project into a third table.

Thank you!