Dear Helpless
I am so very sorry for your pain and how very impissibly hard this is for a mother. We love our sons who have gotten themselves and us into such impossible situations.
I would say this. Remember how you felt when his grandparents were harboring him?
You believed, correctly, that this was bad for your boy. That while what they were doing was understandable, sheltering and protecting him was wrong because he was acting very badly you believed he must face the consequences if his acts. Because this was best for him.
I think your position and choice is the same as was theirs.
In my mind, (but I don't know your child, or you--and don't know more than what you have put in your posts) there is only one right answer but the question is this: What choice would be best for the long-term welfare of your child, for the family, and for the community in general, right now, based upon your son's current conduct and behavior?
This should have nothing to do with feelings, either yours, your son's or his father's or grandparent's. This has to do with an objective situation and objective needs of your child.
If he did not stay in juvenile detention, where would he go, if his father will not take him?
What would be the argument that would be the basis of getting him out right now? How will he get better, without intervention and consequences?
His response after he was restrained, to attack his Dad, looks like he is doubling down. These are violent crimes he is committing. He could escalate. This could get worse.
I think you know what to do. And I think that believing that there may be an answer that could make everything all right and make the bad feelings go away, makes the agony worse. Sometimes the hard thing needs to be faced, and put into the rear view mirror, and with that the pain sometimes lessens. I am sorry.