It depends on how the DPOA is written. Look at the termination clause. What terminates the DPOA? One thing that always terminates a DPOA is the death of the principal. Then, a personal representative is nominated/appointed, but the need for an attorney in fact is obviated by the death of the principal. The DPOA stops being effective. There is no more need for it.
Is his new wife on his checking account as a signer? Generally speaking, that creates a joint tenancy with a right of survivorship in the surviving spouse, and all the funds in the bank account will become hers and not subject to probate.
Also, a will that says she can stay in the house "until she has a place to live" is awfully vague. That could take the rest of her life, or it could be ten minutes. What he may be setting up is called a life estate with a remainder to you and your sister. If that is what he intends, you and your sibling may not inherit until your Dad's wife passes on. If your Dad has any questions about his estate plan, he should call the attorney who drafted it and make sure it has the effect he wants it to have. Many estate attorneys will do home/hospital visits. This is between your Dad and his attorney, though.
If your father asks his wife to act as his attorney in fact, she can do that. However, a DPOA does not allow an attorney in fact to change a principal's will. Sorry this answer is so dis-jointed, I just kept seeing new questions! I hope this helps. XXXXX XXXXX