I may be a little prejudiced in this because I don't think anyone should ever do a probate without a lawyer. Probate, real estate, and criminal law are the three areas that I think a lawyer is required, any of the other areas a person can handle themselves if they are willing to put the time in.
With probate you have a lot of personal liability if even the slightest mistakes are made and the law is complicated, archaic, and often makes absolutely no sense.
I don't think you have to worry about your brother claiming adverse possession (I think that's what you really meant instead of eminent domain) because at this time the property still belongs to the estate and as a co-executor he has a fiduciary responsibility to the estate and that should prevent him from claiming adverse possession.
However, it does sound like he is just living rent free which is against the rules and could get both you and him in trouble since you have the same fiduciary responsibility to the estate which means any property which could be generating income should be generating income.
If you go ahead and get the lawyer now they can both check over everything to make sure it was done correctly, the court doesn't do that even though many people think it is a duty of the judge, and the lawyer can help you move the matter to a final resolution which includes either your brother doing what he is supposed to or the house being sold to a third party.
When you became an executor technically you are no longer supposed to take anything into account other than what is best for the estate and if you do so then you are violating your oath and your fiduciary responsibility.