You could plug multiple SQL databases, but it is not possible to plug a NoSQL and a SQL database in the same project, since they don’t use the same agent (forest-express-sequelize vs forest-express-mongoose). In short, you have to create two projects.
As a workaround, you could (but it will be a long path with some difficult steps) create only one project and consider one database as the main database (let’s say the SQL one is the main). Then you could create smart collections for your secondary database: you will have to manually implement each route using mongoose natively. This is actually possible, but not that simple.
Let me know if I can help you choosing the right path for your need! Also, feel free to add some details about what you are trying to achieve with these two databases: maybe there is some quick-win solution that we could implement for your particular need!