1) Main problem I came across is that whenever I choose the Attack Action on either character and the Off-Hand Bonus Action attack is available, the Attack Action will utilise the Bonus Action as well. Dunno
why that is and it gets really frustrating not having a clue how to prevent it. I can't have any kind of variety in my attacks and fighting style as the Attack Action will consume my Bonus Action as well,
leading to unnecessary overkills and destroying my action economy.
Look for a small little icon below your equipped weapons (to the left of the hotbar). Clicking that should swap between using both weapons vs only using your main-hand weapon with the Attack Action. (At least, I think so. The icon has changed as of Patch 7).
3) Sneak Attacking with Off-Hand Bonus Action SHOULD BE DOABLE as per the 5e ruleset, but as it seems there's a restriction to Sneak Attack in BG3 for it to work with the main hand only, which is not provided in the description of Sneak Attack in game and I found out by reading it on the Wiki. Might be wrong on that last part but if not... Why is it like that ?
+1. Sneak attack should be a toggle that applies on the first successful hit per turn that satisfies sneak attack conditions. Including on opportunity attacks.