Since the database is actually defined at the connection level and SQLExecutor can only use a single connection this will not work.
You could use multiple executors for example:
executor1 = SQLExecutor2(connection='Database1')
executor2 = SQLExecutor2(connection='Database2')
Query1 = "select * from table1"
Query2 = "select * from table2"
Then join the separate data frames using Pandas. As shown in this example
It's also possible to use 2 SQL datasets from 2 different databases and use a Visual Join recipe instead.