Thank you for reaching out to us again and sorry for the wait.
May I ask first, has anything changed about your situation since you wrote us last time? Are you in Germany already or still in Uganda?
I'm not sure if I can give you any other information than our expert Nilab here: How long does it take for Berlin Ausländerbehörde to process for family reunion visa when they receive it?
Looking at different cases from our platform, the waiting time for family reunion visas can be quite long. Once your documents are verified and you receive your visa, you can travel to Germany. You then need to register with the residence registration office and the competent immigration authority.
In order to do so, you have to collect a number of important documents, such as your passport, birth certificate, the wedding certificate, etc.
Please have a look at this BAMF website for a more detailed description of the process that follows: http://www.bamf.de/EN/Migration/Arbeiten/Familiennachzug/familiennachzug-node.html
You may have seen this already, but here is a checklist for family reunion visas by the German Embassy in Kampala (explaining the processing time). https://kampala.diplo.de/blob/1680496/b11fd983e86cf351c2165b3d0a17e33b/checklist--visa-family-reunion-data.pdf
I hope this information helps. Feel free to reach out to the community again if you have any more questions!