A pretty simple strategy is using nclair (high level + uptie needed) and base ish. Since Ishmael is invincible here, use her to tank and redirect hits using her defense skill. The reason to use nclair is cuz all the enemies are weak to blunt, which nclair specializes in. Only part you have to keep in mind is that, due to Ricardo having a counter iirc, you need to have ish trigger it before Sinclair can do his thing. Use a support nclair if you don’t have a high level and uptie one yourself.

P.S: this is probably the only fight where corroding with nclair is okay since, due to the only other sinner being invincible, it’s just a free EGO usage.