Teach him sharing and caring with some stories. Give some examples of sharing and caring. For stories you can use.. Heycloudy storytelling app. Interesting app. With short and simple stories..

You need to teach him sing him sharing is caring song after learning from YouTube or other modes of learning. Play "pass the item" game in which baby needs to pass the toy in his hands and fir 2 minutes play it with 3-4 people together play a tune and start playing this game. Read him bed time stories of sharing love and moreover also check on the part of elder kid is he rude to your baby does a different behaviour in front of you and a different on your back. Trust your baby. Ask him when you two are alone give him time to open up and discuss why does he not like sharing