Different games.
This but the original came out for the Wii/WiiU. Do not bother with the 3DS version I'm amazed that game even exists to this day.
I've played all of the Xenoblade games and I recommend 1 for it's better gameplay/characters. Think of it as a final fantasy universe where the only major connections between games are nods and references.
Nope stand alone games that don't need each other's story to understand one another.
However XC2 has some pretty damn good fanservice for people who played the first game, like spoilers I guess but it's literally in the season pass for XC2. XC1's MC's voice actor came back for XC2.