As a party who has handled a fair amount of estate and probate work in my practice I would like to provide some different insight.
Because Leo and Irene owned the house jointly, their ownership would have been in survivorship form. That means that after the death of Irene, Leo owned the house alone. There is no need to do any kind of estate administration for Irene to pass her interest on to her heirs or otherwise worry about "probate succession". Depending on your state's procedures, it may or may not be necessary to either file a copy of her death certificate or otherwise sign a document that testifies to the fact that she had already passed away.
The only thing that you need to worry about now is getting the house to Betty. Because Leo died owning the house solely in his name, it must pass as part of his probate estate. Both Betty and his children will be heirs to his estate. (The exact proportions will depend on the laws of his state.) (It doesn't matter who lived there, or for how long, etc. It is not the strength of ties that a person has to the property that matters but the fact that they are related as spouse or child to the person who passed away.) That means that mom would end up owning part of the house by inheriting it under the probate process, but the kids would own the rest. In order to own the entire house she will either need to buy out all the different kid's interests, or they will need to gift/assign their interests to her. That is certainly feasible, and we have done it in estate administrations often.
I bring these points to your attention so that you have a better concept of what the issues are (and are not). As a party who handled a lot of probate estates, I can't argue with the advice to see a probate attorney to help with this. But I would suggest that it would be worth everyone's while to have talked ahead of time about whether some or all of you want to gift/assign your inherited interests in the house to mom. That will tell you what kind of procedures that will be needed.
I hope this has been helpful. Let me know if you have any followup questions. If none, please remember to click on the ACCEPT link so that I may receive credit for working on this topic with you. (I'd greatly appreciate it!)
Thank you,
Dan
--------------
The information provided is general in nature only and should not be construed as legal advice or to create an attorney-client relationship. You should always consult with a lawyer in your state.
PS: If an answer appears to you to have been very helpful, or to have taken above average expertise, and/or research, or if the answer shows an above average amount of time and dedication devoted to your issue, a bonus is nice way to say "Thank you". Thanks!