They look fine to me. Attached is an in person example of Brian Wilson and Al Jardine from October, 2016. I'll see if I can find an image of my Mike Love. Brian's signature is often very rudimentary, but Al's is typically very nice.
They are indeed 100% authentic as I was the original owner and obtained the autographs in-person myself. Here are my photos from getting the autographs. Shane obtained this album in a trade with me.