Not if Alberto was the 2nd choice all along. Besides chances are if Maroni took over directly he was Falcone's consiglier or something similar. Maybe Falcone's cousin, so it arguably was the family. What you would want to imply is that Alberto is someone who is mentally imbalanced and was passed up, until he was the only choice. (Some how surpassing Sofia and Mario, possibly putting them under a house arrest kind of deal).
As for Buscemi not being passable as Wilkinson's son, your probably right, he is less then ten years younger and doesn't bare any resemblence, but thats what we have make up for.