Windows can be added to each copy of Grub; there may or may not be a way to add other copies/types of Linux, I don't know, but it doesn't happen automatically
Usually you can. The tricky part is that I was effectively installing two copies of the same OS in parallel, which an automated installer can't really do in the same place without name/reference conflicts
The consensus of Ublue / Red Hat / OS installer / general OS development people here regarding a lot of things I have done was "nobody ever does that, I have no idea"
When I asked about the possibility or methods to install things certain ways, it was because my personal situation warranted the attempt and risk, but the response was not "there is a risk and we provide no warranty or guarantee of success"
The stance y'all adopted of being solidly and somewhat aggressively against same-drive dual booting under any and all circumstances instead of emphatically neutral and non-liable came 6-8 months later