Starting Over with a 5 Year Old

My 57M brother has met a nice young lady after 17 years of marriage which ended in divorce. His first wife had 3 daughters and they had another daughter together. The new lady is 39 and has a 5 year old whose dad is not in his life. He really likes the lady but after his first marriage where he practically raised his first wife’s children he’s hesitant to move forward with the new lady. He is asking me for advice and I wanted to hear from this group what your thoughts are.