OOC:
Hmm, good question, can you ready an attack form a spell that attack on its own? Can you still do so while using an action?
Edit: Alright, after some reading, here's what I got. Readying an action takes a standard action, so you cannot cast a spell which requires a standard action and still ready a standard action.
Also, about Spiritual Weapon "attacking on its own", you still need to direct it. You cannot direct your weapon to attack a target you cannot see.
So this is how I interpret the current situation. You need to ready an action to direct your weapon to attack the otyughs when their tentacles shoot out. Once the weapon has been directed, it will attack the otyughs all on its own no problem. So right now, if you want to ready an attack with your spiritual weapon, you need to ready an action to direct it towards the otyughs, and you cannot do that if you cast Bless this round.