When my friend and I played in your mod, it really put us off for a few reasons.
- They only target one player, and after killing them, the boss disappears.
- Sometimes you need a lot of resources to mine, but it's incredibly difficult, takes a long time to camp, and it becomes boring.
So my suggestion is to make the bosses target the person who deals the most damage, so if one person dies, the other can continue fighting.
And maybe make mining easier somehow, for example, by adding a pot that shows ores or increasing the spawn rate.