Can an Executor of a Will act as a witness for that Will? And can that executor provide one of their own relatives as the second witness?

Our mother has made a Will. She is 86 years old. The family have concerns about our mothers mental capacity and she is currently in residential care home being assessed because of concerns regarding this matter. She was appointed to Social Services by a hospital who treated her for a fractured collar bone after she had a fall in a supermarket. The hospital treated her for the fracture, but had some concern about her mental health as she insisted she was not in hospital, she claimed to be on a holday in Spain! And so they contacted Wolverhampton Adult Social Services who are placing her in residential care for 2 weeks while they assess her.

I tried to speak to the Solicitor about our concern for mothers mental health, but only got told that it's our mothers money and she can do whatever she wants to. They provided 2 witnesses, the Executor being one of them,and a relative of the Executor being the second witness ( both witness surnames are the same )

Is this legal and binding?