SR6 also has errata coming in this month, and part of the backlash against it is simply because it changed up a bunch of mechanics significantly. There's also some places where they made a mistake converting from SR5 to SR6, but those you can ask us about and get simple quick solutions (assuming the errata don't rebalance those spots).
Honestly, if the entire group is new: Get SR6 Core, and once Firing Squad (the combat book) is out, get that. The whole 'books come out over time' will be perfect to get back into things for y'all. Since you're coming back from an entirely-different Matrix, having just one base book for the Deckers for now sounds like a really good idea.
If you want to know 'what's what', there's the Anarchist Streetpedia as option (on top of, of course, the
Shadowrun wiki), basically an encyclopedia with a lot of in-character responses in it covering a lot of things. Cutting Black is almost out and is basically 'holy crap these big things are going down', the book is chaotic apparently but it completely changes up the UCAS.