if you need help with the gemini 2 it is better asking at aussiex because that was the website where it was made and can be downloaded from.
However i am able to help as well with a few things - the destinations will be have you correctly installed the Fonts folder. the bell will be a missing .wav file if you have the London Citybus 400 try and take the stop bell.wav or similar from the sound files and put them into the Gemini 2 sound folder the lights i don't know but if these options do not help then it will be a corruption of files on download if you go back to the download site you can redoenload it and if you get a network error don't click resume delete the file and REDOWNLOAD IT!!! and make sure you install everything correctly usally files will come with a folder called OMSI 2 at the start and what you do is just drag that folder into your common file for steamapps
I think some of the interior light switches have 3 positions instead of 2. Try turning them on a few times. The default keys are '6', '7', '8' and '9' on your keyboard, providing it's of a standard British layout. When it comes to the destinations, you are probably missing the dot matrix .bmp file. It was missed out from the original download, but is available separately in a post on the 'OMSI British Buses' Facebook page. Make sure you put the .bmp file in the right place.
It sounds like your download is not complete. By not working, do you mean it doesn't make a sound but still activates the stop request, or the bell just doesn't function full stop. Try redownloading the whole bus, from the base version.