6 month old and sleeping

Hi everyone. My baby boy is 6 months old and just will not sleep through the night! he has me up between 4am and 5am everyday and just will not go back to sleep, so I'm exhausted! I also have a 19 month old daughter who he also wakes up when hes crying! I do the whole bedtime routine, bath, night time porridge and bottle but nothing seems to work. He's also on 4 meals a day. It was that bit easier with my daughter as she takes a soother, so that helped alot. I know in the long run its better if he doesnt have a soother but sometimes right now i wish he did! Can anyone help? Thanks :)