Is Jacob immortal because he imprinted on Renesmee?

Because Jacob imprinted on Renesmee. The imprint means he'll always be there for her in whatever capacity she requires, so if she's immortal, he will be too. He stopped aging until she catches up to his age, at which point I think they'd both be in their "final form".

Why is Renesmee nicknamed Nessie?

Her middle name, "Carlie", is a portmanteau of Bella's father-in-law, Carlisle, and Charlie, Bella's biological father. Her full name is Renesmee Carlie Cullen. Jacob Black gives her the nickname "Nessie" because he thinks her full name is a "mouthful".

What does it mean Jacob imprinted on Renesmee?

In Jacob's case, he imprinted on Renesmee — who he affectionately dubbed Nessie — when she was a baby, so no, it doesn't mean he's in love with her. Jacob just has a strong bond to Renesmee and is more of a protector and as she gets older, will be a best friend, someone who's there for her when she needs it.

Why did Bella name her daughter Renesmee?

She named her daughter Renesmee because she wanted bothe esme and renee to be in the name. Then her middle name is Carlie which is Charlie and Carlisle together. Plus Bella and Edward were married so it was very smart of her. The reason she named her baby Reneesme was because she thought it wasn't fair...