Clean Installing MacOS on 2011 11" & 13" MacBook Airs Predicament

OK so this may be a bit confusing for some so you may need to read this a couple of times :) as I have some MacBook Airs from 2011 that I have managed to recover back to full working condition BUT I do not know what was the last OS that was installed on any of them. We can all agree that they were originally released with OS Lion 10.7 & they all can support up to 10.13 High Sierra. I have bootable installers for every OS from 10.7 Lion on wards ready....)

1/ I have managed to mix up their individual SSD's and so am unable to accurately determine what was the last OS that was installed on any of them, so I will wipe the drives clean anyway before clean installing the OS again and avoid causing the dreaded "Failed to load EFI driver issue" as I have a hunch this can be caused by jumping to far ahead with OS versions and their firmware updates, OR indeed 'rolling back' versions. Am I correct?

2/ I was aware that High Sierra & Catalina (Not supported) had firmware updates included in the installers.... and that I am 99% sure for example that you cannot go directly from Lion to High Sierra. I maybe wrong on this. Never tried.

3/ But what if these previously had say High Sierra installed, can I roll back safely to Lion?

4/ Which of these supported OS had a firmware update included? Lion, Mountain Lion, Yosemite, Mavericks, El Capitan, Sierra, High Sierra.....

5/ How would you safely go about updating from 10.7 Lion > High Sierra? Am I correct to say it must be Lion > El Capitan > High Sierra? As Here is a thread I stumbled upon regarding a similar situation.

I haven't dealt with versions of macOS that old for a long long time so hopefully someone else can remember & can fully understand this predicament and give me answers to all 5 parts :)

I intend to give these away to the kids as they won't care or notice they are old or whatever, they will more than likely just use them for Facebook Messenger & YT no doubt..... and be happy to show off they have an Apple laptop :)