California law, of which I don't know the specifics, would have to be superimposed on all these suppositions.
I believe that under California "usual and cutomary" deed construction they likely recorded the deed as being owning the property "by the entireties" which is the same thing as "joint tenants".
Scott may own the house, but the personal property in the house would go by inheritance, I think. Scott does not necessarily own all of THAT.
California is a community property state. Both of the parties own the properties. Kind of like the joint tenant an by the entireties concept in real estate ownership. Absent a will there is really little or nothing to decide.
There is of course no need for the Rochas to have a power of attorney as regards Laci; I'd think they would simply apply to have one of them be the representative of her estate.
Scott is Laci's next of kin by virtue of marriage- not Laci's parents. Given that Laci died intestate, there is no formal estate that they can administer or be the executors of. Even if there is some identifiable "separate property" (maybe a pre-nup?) I don't think that there wouuld be a situation where this could occur.
When the presumptive heirs (the Rochas) to property have reason to believe that someone is going to "waste" the property, seems to me that they can get authority from the probate court to take measures to safeguard the property. I'm talking about Laci's personal property here. Wonder if the Rochas have anything pending in the probate court to try to cause a sequestration of assets, a safeguarding of all the assets subject to inheritance.
Unfortunately, the Rochas are not the presumptive heirs- Scot is the estate, he is the heir at this time. That will change, of course, if he is convicted for Laci's murder.
There is no probate case for the Rochas to file an action under. The easiest way to tie the house up if someone tries to transfer ownership or sell it, is really simple. They should file a wrongful death action against Scott and file a lis pendens against the property. No one in their right mind would buy the property then.
As I know you are aware I do not support Scott Peterson, nor have I prematurely found him guilty. What I find somewhat distasteful in the house plundering incident, is that Geragos had already agreed to allow the Roches into the property. I believe that was to be this coming Tuesday. (I'm sure that someone will correct me if that's the wrong day.) I think that he wanted to document what was removed by the Roches. It appears to me that Mrs Roches, for what ever the reason, had an attack of temper and jumped the gun.
Just a point to ponder. If the Roaches had the legal ability to enter the home and remove property, why on Earth did their own attorney tell them not to???