Room Sharing with a newborn and toddler Help!

I really wanted advice and help to see what would be the best suggestion on what to do as far as sleeping arrangements for new baby coming in October. My toddler girl will be turning 3 and her baby brother will be born in October. I have my toddler sleeping in our room in her own playpen. I wanted to also bring in our newborn to sleep on my side and toddler on my husband side in their own bed or playpen. What suggestions or experience do you all have? Should I put the toddler out into her room? My mother in law thinks to wait before putting the soon to be 3 year old alone in her room since she said it causes resentment. She told me it might make the toddler believe that she’s not wanted anymore and that new baby is. Should I room share with them both?