Yes to any or all of those options!
Siblings are such an important part of a newborn shoot! We have thought of many ways to engage siblings so we get images that are meaningful. You can have siblings present for the whole session, or some families choose to have siblings leave with a grandparent or sitter after the first hour.
Grandparents are welcome to be in a few shots. Many families love to have pets for a couple of shots as well! We have experience and ideas to help you set this up so it goes safely and smoothly.