Taking a baby on a plane and to Disney

So before I got pregnant my husband and I planned a trip to Disney with our other two children. We still plan to go but we are conflicted if we will take #3 or not. When we go the baby will be 8 months old. Has anyone taken a baby this young on a plane? To Disney? My MIL offered to watch her for the week we’ll be gone, but I really don’t think I can leave her for that long. I’ve never left any of my children for that long. Just looking for advice I guess.