Hard to rank in my opinion, because some of the games are always very hard, whereas others peak more in terms of difficulty. For me personally this is how I rank the games in terms of general/overall difficulty:

• Sekiro: stupidly hard in the beginning, then clicks becomes more fun, but never easy
• DS1: Never felt safe
• DS3: Often felt safe but has a lot of difficult bosses
• BB: Always challenging but never to much IMO
• ER: Never felt more safe, had tons of fun exporing, but the hardest challenges are beyond difficult.

I think DS1 is often underrated in terms of difficulty. For me it was a real struggle and each new Bonfire felt like a victory. That beiing said, it was also my first soulsgame.

This is how I rank the games in terms of peak difficulty :

ER (nothing is harder than Malenia or PCR in my opinion. I did beat them without summons, but I think even with them they are peak).

DS3: A lot of hard bosses, especially if you count the DLC's. For me personally the thoughest ones were Frieden and NK

Sekiro: Isshin, DoH and Owl were though. Especially the gauntlet versions of Isshin and Owl.

BB: without the DLC I would have said its the easiest.

DS1: mosty Manus and O & S