What happens in case I install the Passive BLE in parallel? Do I see the sonsors twice?
Possibly or one will not work. The last time I tried this, only one worked at a time due to active polling, which if I remember, correctly takes control over the bluetooth adapter where passive subscribes to events. I believe Passive BLE Monitor changed libraries where Govee devices are seen with a passive connection. There may have have been library updates that allow both to work in tandem. You can try and see what happens, the data shouldn’t conflict.
Do you have any suggestions how to access the sqlite DB in a comfortable way
If by “access”, you mean strictly accessing the data, you can interact with sqlite database directly.
If you mean view large amounts of data in the dashboard, unfortunately no. This is a problem I have run into a few times where I lose a year’s worth of data do to corruption but haven’t dedicated enough time for a solution. The SQLite data base is primarily meant to be a short term data store. Overtime, the overhead will become too much, especially if writing to a sd card as it is only a single file database. I also tried a MySQL database recorder but had issues with migrating data. My last attempt was to use SQLite as a short term record, may be a week, then purge the data while recording the information into a time series database like InfluxDB so I could explore the data independent of Home Assistant but I didn’t get too far with this. As I never found a solution for myself, I am not sure what to suggest.