My DH and I were living together by 18 months (which I know is terribly frowned upon by mumsnetters generally, as mothers are supposed to stay single for a very long time & then even if they meet someone they are not allowed to introduce them to DC for over a year, and then God forbid that their partner moves in as the man is probably a sex offender..)
But, anyway… to answer your question, my DH was getting quite involved by that stage, he enjoys doing things with the children and we were starting to operate as a family unit. He also saw me juggling with everything and wanted to help out.
He has brilliant relationships with the DC’s now, many years later, and that has developed as he has been so present and so he knows them really well.
He does school runs/pick ups and drop offs to friends and clubs etc. He sat by the side at their swimming lessons or stood by the side of football pitches, when they still did those things. He helps with homework when he can (but only really the craft stuff as he enjoys it!)
When they were still at primary he attended nativity plays & sports day etc.
He will take them out for days, with or without me, and he takes time off in the school holidays and emergencies, so we are sharing that load. He is currently teaching my eldest DS to drive.
We share daily washing/cooking chores although I am the one who gets them to tidy their rooms. I still did bathtimes when younger and I do the medical apts - although he has taken one to a GP at some point, when I had to work.
We share everything really. He does everything I would hope a good biological father would do.
My DC do also see their dad, every other weekend, but he isn’t interested in giving up his “free time” outside of that, and never really wanted to be a hands on parent to start with, so there certainly hasn’t been a conflict with DH overstepping with anything their dad would want to do.