Do a little experiment with someone having common letters in their name and to your name ... write your full name then have someone write your full name right below that, then you write the other person's full name below their writing of your name.
When you locate a letter within the name which is common to your name and the other person's name, you will note that you wrote that letter the same pressure and sweep in your signature and the one you wrote of the other person's name.
I agree with you. To me it is obvious that the same person signed those. Wouldn't you know the third signature is unreadable. Let's not forget that Madelyn mispelled her own signature!!