Split database for security and privacy reasons

Currently I have a small business where I have a main product (written in PHP and MySql), several users, several companies, etc. The software occupies around 20 tables in its operation. The problem is that I want to expand the business and create a different program, but I want to unify the data. A new program (different function) will use about 30 tables, but in reality there is a "core" that are the same tables, let's say 10. Here I have two options: * Create a larger database with 20 + 30 tables, (since some were repeated) = 40 tables. * Or create different and connected databases DB_core = 10 tables DB_1 = 10 tables DB_2 = 20 tables Why using different databases? I already want to develop this second software with a different team, but I don't want to give them access to some sensitive or valuable information, tables of people, companies, etc. This data will keep it in the "core" database and only in the production server. From what I understand, users can be created with permissions by tables, but I feel that it is much easier to keep us in separate databases. Are there any significant performance implications? Is the most extensive programming worth it? PD: Sometimes, I need the programmers team manage the production server.