How do I get temporary custody

I agree with all the other lawyers. You need to get a lawyer on this immediately.

Is there anything I can do to stop this from happening?

There has to be something out there that made the judge keep the siblings separate. There are a lot of questions not discussed in your post that...

How can a father still be required to pay child support to the mother, if that child is grown, married and employed?

It's possible that he's still paying child support that was already past due. But he/you need to check into this. If he's paying through DHS,...

As the fiance, what are my legal worries, could i be put on the stand about my character or is it all about him and his issues?

Yes you may be called to testify since you have knowledge about the matter.

Can I counter sue for divorce from Mississippi now eventhough magistrate has made final ruling on divorce but it isn't final yet

You need a new Ohio attorney pronto. You may can appeal the decision and get a second bite of the apple, but it'd have to be done in Ohio.

How long after the divorce should I pursue child support? Can the courts order her to work or place some monitory lean on her?

You may want to go back to court and do some modification to the decree. You'll need to speak to an attorney in person because there will be many...

Where do we go from here to assure that our grandchild remains in our care?

It doesn't sound like you have too much to worry about. A "cash" job is not stable under the law in that situation.

It is possible to do what you are wanting to do...just not the way you want to do it. You'll need a lawyer and any changes will have to be court...

Will the guardianship terminate by itself when he turns 21 or will we need to file something with the court?

Mr. Freeland is exactly on point. You need to shut it down properly in order to not have unnecessarily complicated things.

Can I request a trade in or get my money back all together? I just don't trust this dealership now.

If you've already signed all the papers, they are going to give you a hard time about "getting out" of the deal. They will probably tell you they...