It is legal, but it raises red flags.
In the United States, you can do whatever you want with your money: give it to your neighbor, your lover, your church, or the society for the protection of beetles. You can do this during your lifetime or have it take effect after your death. But that is assuming you know what you are doing and are acting under your own free will.
If you are cognitively compromised or under someone else’s undue influence, then you can no longer give your money away so freely. Giving money to a financial planner and his children raises serious questions. He is not what is often called the “natural object of one’s bounty.” And he has a confidential relationship with her, advising and guiding her on her finances. That means that if someone challenges these gifts in court, the financial advisor would probably have the burden of proof to show that your mother was legally competent and he did not unduly influence her.
But it isn’t an open-and-shut case. For example, his case would be strengthened if it turned out that he knew nothing about the will.