Katoslake
Recycles dryer sheets
There is no need to worry about taxes for heirs assuming that the investments are in taxable accounts (not in traditional IRAs), which I suspect is likely from what you wrote.
Obviously, the $750k in checking is very suboptimal, and unwise if it is at one bank. I'm guessing that she earns negligible interest on her checking accounts. The first thing that I would do is to take her and her checkbooks to your local Schwab or Fidelity office and set up a brokerage account and transfer at least $700k of the $750k into it... more if she is agreeable to it. The brokerage firm can then help you put in place a 4 year ladder of CDs or US Treasury securities that will likely yield 4.25% to 4.70% and generate about $30-35k a year of interest income. When you help her set up the brokerage accounts she can set up the beneficiaries of the accounts... who will get the money when she dies. She'll need their names, addresses and perhaps their SS#s.
While it is tempting to sell the Columbia shares, hold off until you know what the basis of the shares is. Columbia or her broker if they are held in a brokerage account should be able to tell her the basis depending on how long she has had them. Once you know the basis you can determine the gain if she were to sell them and the tax on the gain on the sale. When y'all talk with Columbia or the brokerage firm you will want to ask if she can designate beneficiaries for them and if so get the paperwork started to do that so the assets doesn't end up in probate. The stock will get a stepped-up basis when she dies so the beneficiaries can then sell it tax-free.
On the house, if she is in Texas like you are she is lucky that Texas is one of a handful of states that allow enhanced life estate deeds, also known as Lady Bird deeds. She can have an enhanced life estate deed written by a lawyer designating the people who she wants the house to go to when she dies. Technically, she transfers ownership of the home to those "remaindermen" but at the same time retaining a life estate that allows her all the same rights she has as the owner... to live there, to rent it, to take out a loan on it, to sell it and keep the proceeds from the sale, etc. When she dies then the life estate goes away and the remaindermen become owners of the property without the encumberance of her life estate.
From what you wrote you should be able to arrange her affairs so she can avoid probate when she dies and her assets will go directly to her designated beneficiaries without you having to go to probate court. Also, her investments should be generating much more income for her.
Thanks for your comments and advice. Will encourage her to move forward.
It will be hard to get her to leave her banks due to her long relationships with those buildings. Not the people, but the locations