This is so cool! Although the Sabaton and Nightwish Army are supportive, you should know they've taken a particular liking to you. I've never seen them press the Like button this energetically.
1. Did anyone specify whether they requested Carolus Rex in Swedish or English? Knowing the Sabaton army, they'd probably scream "Review BOTH!", but whatever rocks your battleship. There are, to my knowledge, only lyrics videos and fan made videos of these, but they're decent.
2. About Sabaton's Livgardet and The Royal Guard: they're basically the SAME song in Swedish and English, respectively. The lyrics are somewhat different (there are quite good captions, though!), but the music's the same. The music videos are not the same; weirdly enough, the Livgardet music video seems to be a either the beginning or the end of the story told in The Royal Guard mv. Hard to say, I think Livgardet is the ending, but I'm honestly not sure.
⠀⠀The song was written to honour the Swedish regiment Livgardet (The Royal Guard), one of the oldest military regiments in the world, which was established 500 years ago this year.