How can we teach our baby to sleep so he doesn't wake his brother?

Self Consolation: Between four and six months of life a baby has the ability to learn the skill of self consolation, this is an important life skill for parents to help their baby learn! so you'll want to put the baby down after your evening routine and last breastfeeding/bottle when he is sleepy, yet not asleep! he will learn to suck a thumb, rub a blankie, twirl his hair, etc... And console himself.

Put him down awake: He needs to learn to soothe himself to sleep. You can get him bathed and fed and rocked and ready, but put him down while he's still awake. Even if he cries at first, he will "remember" falling asleep in his crib, and be much more likely to sleep all night.

Avoid night activity: Babies over 3 months old can usually be trained to sleep through the night. The younger babies might go 6 hours before feeding, but the older babies should be fine until breakfast time the next morning. Do the same relaxing bedtime routine each evening. Put the baby in the crib, say "goodnight", and walk away. He might wake up off and on and cry but will learn to fall asleep by himself soon.