My mother in law died several years ago without a will. Then last year my wife died. We were not living together when she died. We never divorced. Now I find out her sister sold the house her mother owned when she died. Is she to notify me and is the real property partly mine.
How do you know that your wife's mother died without leaving a will. The only way you could know with any degree of reliable certainty is if you have personally searched and examined the appropriate county records wherein she was living at the time of her death and there discovered that her estate was probated and or somehow summarily administered, distributed and settled as one of intestacy.
And if you had done so and found any such filing, its reasonable to believe that you would have also learned what assets remained in mother's estate and what, if any part thereof would have vested in your wife and/or her issue per intestate succession.
If you have not made any such record search, how do you know that mother-in-law owned anything at the time of her death. Just because the sister may have sold a home once owned by her mother is no evidence that she or your wife inherited any part of it.
It has been suggested that if prior to her death your wife succeeded to a partial ownership in her mother's home that some of it (appreciated value) might have been transmuted from separate to community property with you having a vested 1/2 interest. Although I do not agree that passive appreciation in the value of a spouse's separate or non marital property necessarily converts it to marital or community property your wife if then living may have feared so. And as consequence of the estranged relationship could have easily voided that possibility by renouncing any rights to the home. And possibly with a side agreement to share in the sale price.
Anyway in my opinion the only sound advice you have received comes from justalayman. So get busy and start tracing the two estates. If any such be.