I'm struggling with the concept of 'training' & 'baby' since in my view (I'm old remember...) the baby time is largely about instinct.

Babies are small animals - they cry if they're hungry, in pain, uncomfortable or bored. So you feed 'em, change them & play with them. By & large a baby makes her/his own routine & forcing anything is unwise.

Babies in with parents is a matter of choice. As seaivy points out, things were different in 'our day' lol! My babies slept in their own rooms after six weeks & thrived. But unlike most mothers in those days, I carried mine in a sling quite a lot. I liked to have them close.

I was lucky - happy babies & no horror stories. There is IMHV, far too much interference from self-important 'experts' nowadays, & an obsession with weight gain & milestones etc. So long as they can tie their own shoelaces & go to the loo unaided by the time they go to school, they'll be fine.