Hey there! I totally get it, sometimes paring down descriptions and information can make things more difficult. Apologies!
You’re spot on with diminished and enhanced attacks. If an attack is diminished, no matter the weapon or attacker, the damage is reduced to d4. Likewise, if an attack is enhanced, the damage is increased to d12.
For damage advantage, you roll the damage die twice and take the higher result. So, if you rolled a d6 twice and get 3 and 6, you’d take the 6 for damage.
I hope this helps clear things up. Thanks and all the best!