There's a very slight risk of inbreeding, but it's really not as bad as most people think.
In many cultures, first cousins are regarded as ideal mates.
brother
Your nephew's baby would be your grand-nephew or grand-niece. You would be their grand-uncle or grand-aunt.
The child of your nephew is your great nephew (if a son) or your great niece (if a daughter).
Your sister's son is your nephew and you are their aunt or uncle. Their baby would be your great nephew. Some use the term grandnephew, but great is more accurate.
if she has a boy, then its a nephew. its she has a girl its a niece.
Your nephew's daughter is your great niece. Her child is your great great niece or great great nephew.
Your sister's son is your nephew.
Your brothers baby boy is your nephew
Same way as human mothers
That's actually a common age for mothers. There is nothing wrong with a 20 year old parent, if they are able to take care of the baby.
Your Nephew :)
Most mothers have the baby because they love their husbands and want to share that love with children.