In general terms anyone is free to gift a house. The main exception is that if a person is made bankrupt and makes a gift at any time 5 years before bankruptcy to a connected person, the trustee in bankruptcy could challenge the transaction. The scenario you describe is perfectly valid. The man owned the house outright on th death of his first wife. His second wife had left him for a period greater than two years so she no longer has occupancy rights in the house nor did she ever share the title to the house. The man transfers to his sibling during his lifetime. Then he dies. The sibling owns the house. That is unchallengeable by the estate. I hope that helps. Please leave a positive rating so that I am credited for my time.
I'm not sure that I can answer this in a way that would give you the remedy that you want here. The fact is that he transferred the house to the sons and this wasn't undone before he died. A verbal agreement is meaningless in the law of Scotland where houses are concerned. Contracts and agreements have to be in writing. So if something was supposed to have happened, ie, the house was to be transferred back and it wasn't transferred back and there is no written agreement that it was to be transferred back, then there is no legal right or obligation for it to be transferred back. The estate would lose any court action if it tried to claim the house, I'm afraid. This man has taken steps to protect his house from his estranged wife and he has succeeded.
You have your answer. I can't add anything more. I can't invent the answer that you want. The man owned the property. He decided to transfer it to his sons. He was entitled to do so. What he said verbally is totally and completely irrelevant. A contract involving a house must be in writing. You can go to a reference library and look up any book on property law and it will tell you that. Start with Professor Hallidays book if you want a legal reference. Then look at Professor MacDonald's book or Professor Walker's book. The law on this is several hundred years old! And yes it probably can be found on the web, I don't know. This transaction, entered into freely by your father, cannot be challenged or made void from the information you have given me.
1. The person has to be the owner of the house. 2. The person must be sane and not inhibited by any court order or bankruptcy. 3. It can only be challenged in the circumstances outlined in 2.