Triple boot Grub editing

I have Zorin, Solus and Win 10 playing nicely on a triple boot system. Fortunately the Solus install picked up Zorin and added to menu. Two questions

  1. Which grub file/partition do I edit to change settings on the boot menu?
  2. Will Zorin update the correct grub on kernel update or doesn't it matter?

If your Zorin OS is the GRUB file that is in use you edit it in the terminal with:

sudo nano /etc/default/grub

or whichever Linux OS is using grub, you edit it in that OS.

As for kernel updates on different systems, it might be worth updating GRUB if Solus OS has a kernel update, then in Zorin:

sudo update-grub

Thanks for that.