The judgments against your father are now held against his estate, including the house. It's probable (but not definite) that your parents held title as tenants by the entirety, which is to say, as a single marital unit with automatic right of survivorship to the surviving spouse. This means that your mother automatically inherits the property, but the liens are not considered satisfied, as they move with the property. Since it's likely that your parents held the estate jointly, it wouldn't matter that one of the owners is deceased.
Either way, the IRS is going to get theirs. What could happen is, she might sell the property subject to the IRS liens, lowering the sale price and passing the lien on to the new owner, who would agree to assume responsibility in return for the lower price. Or, if the new owner does not agree to assume responsibility for the lien, the IRS would take their share out of the proceeds.
No matter how the title is held, at least half of the proceeds will be subject to seizure by the IRS in satisfaction of the lien. I'd need to know some more information to be able to give you useful advice. I'm pretty much in the area of generalities at this point.
Feel free to call me, or any other tax/real estate attorney in PA, for detailed advice. I'd be happy to go over the details with you.
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It is likely that your father's share of the proceeds will go to the IRS. Your mother should talk to a tax attorney. Many offer a free consultation.
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