You are not going to do that with rehearsals that are that too far apart, you will have forgotten all the nuances that you need to lock into your brain in a week, never mind two weeks... Once they are locked in fine... they should stay put, but you need regular repetition at close intervals to get it in there.
Until they put themselves in your shoes, and realise that you all need to ‘woodshed*’ together to get it locked in you are in for a long tedious fight...
Thanks, Nick, for your very thorough and wise comments; I think the same, and I started the topic to make sure that I'm right.
The part I quote from your message may be the most important thing that I've been trying to make them understand, but they won't. So it really is a long tedious fight.
I sometimes wonder why I don't quit them, but then I think how much my skills have improved these months, and I sort of take the whole thing as a good school with strict and blockhead teachers who teach you very good things even though in the wrong way. And since I've been with this band, it's much easier to play well and do nuances with my other band.