I don't think the government will have ownership of the homes. At least not in any more sense than the bank owns your home. They (govt or private bank) owns the lein on the property, but the homeowner "owns" the property. The homeowner is responsible for the taxes, not the bank that loaned them the money for the house. The bank does have a legal interest in the home, but they do not "own" it in the general sense.
Default on your mortgage and the bank will take the ownership away from you (forclose). If they had actual ownership all along, they could not take it from you if you didn't pay.
What the bailout is supposed to do is allow the govt to buy the "bad" debt from the failing banks. Supposedly (as we are told), the only thing that will change is the name on the paperwork of who holds the debt, nothing more. But there is always the fact that the govt has told us one thing and done another in the past to temper our faith in their intentions.
The authority for the govt to bail out Wall Street (or anybody else) comes from the general ability of Congress to pass any bill they so desire, and with the President's signature it becomes law. They can do anything they want, as long as it is "Constitutional". And we have a mechanism for examining laws and determining if they are constitutional. The fly in the ointment is the time it takes for challenges to reach the Supreme Court, the fact that the Court can refuse to hear a case, and ultimately, the concience and integrity of the 9 justices.
As the recent Heller case shows, things that are clear cut common sense to us can be narrow decisions (and go either way) to the High Court. And history shows that the personalities of the men and women making up the court are at least as important to their judgements as the written law itself.
So, Congress can do as it pleases, until the court says they cannot, or until the next election cycle, where the people have the chance to change Congress, if enough of them desire it so.
All else being equal (and it almost never is) bigger bullets tend to work better.