Gift of rental property

This isn't an answer to your question, and you may know this already, but it would have been much better for her to sell (on an installment sale) or lease the properties to her grandson, and then let him inherit then when she dies.

I know that we don't have all of the details, and there 'might' have been a valid reason to have done it this way, but to Stu's point, the son now has properties with a low basis, possibly close to zero, and a huge tax bill on the sale of any of these.

On a personal note - same thing happened in my family. Grandmother died, transferred house to father, well before her death. Father to mother, long before he died. I had a long talk with mom, told her the way to protect the house was to put it in a trust for my sister, I offered to pay the cost. She ignored the advice and the family lawyer transferred to my sister. Now, mom passed 5 years ago, and sister has a house with original basis, $4000, instead of the step-up to about $1M. I'm a cynic, and unless I know why the lawyer did this, I'm not harboring good thoughts about him/her. (If it was for medicaid/ nursing home issues, there's still a lookback provision, 5 yrs, I believe)

Sounds like the lawyer did this because that is what your mom instructed him to do. Likely even after he gave her the same advice you did. I have seen similar.

And the lawyer may well not have properly educated his client. I've seen too many lawyers who know nothing about estate or tax planning, advise on those matters and cause problems that can't be fixed.