What is a good level to get to in order to fight the twins
Id say about what you were at to fight the final boss
85 all around with a yoshitsune equipped and you should be fine, also I can't stress this enough: MAX OUT HIMUFI'S CONFIDANT. switching party members mid battle is practically necessary to survive.
Level around 80ish and wait until around December in the game to fight them.
Well, due to the mechanics of their boss fight, and the availability of yen- based persona summons in NG+ early on, it is actually possible to beat them before hitting lvl 10. Spoilers below, I suppose.
This is done by persistently switching personas to avoid getting knocked down, as like other velvet bosses, the twins have a pattern to the attacks they use.
The twins, as you may have realized, exploit weaknesses to gain "1 more's", and fighting them with extra party members can sometimes make the fight harder. Your main concern should be preventing joker from taking damage, and preventing the 6 turn AoA.
All mechanics to their fight are of course, on the wiki page, under "strategy".
In short, although it may seem like a great idea to level grind beforehand, it may not actually make a huge difference, so long as your personas are fused with the proper abilities and passives. Feel free to, however, because it might still be fun to bring all of the phantom thieves in!
Here is a video of omega soloing it without yoshitsune or kaguya: youtu.be/57JAxSTqnDw
What do you think?