Toddler and new baby

Latanya • I’m a Social Worker-elderly and disabled population. i have two boys ages 4 and 2 with boy/ girl twins on the way!!!
Any advice on managing a toddler and new born.. I'm only four weeks but I want my toddler to understand that he will have a sibling.. Yesterday I was holding my nephew and he got so sad he starting crying and stormed off... I don't want him to feel lefted out when the new baby comes 😔