I've been "co-parent" with my son for the last 5 years. My son got his children full-time at that point, when they were 5 and 9. He was only able to take them on that understanding, ie that I'd be there morning and afternoon, every day. I get up at 5am and go over there when he leaves for work, do the morning routine and take them to school. Then at 2-30pm I head off again , pick them up, take them home and prepare dinner. When he gets home, I head off home.
I do all the school things, teacher interviews, buying uniforms and books, helping with homework. Make all the appointments, take them to the doctor etc. I'm the "mother figure" to them and we all dearly love each other.
When my granddaughter got to puberty I did all the " growing up" things, we watched You Tubes together about periods and I demonstrated how to use pads, lol. We both saw the funny side of that ! I was very pleased when she did get her periods and she said that it was all very easy "because Grandma showed me how to do everything". Comments like that make it all worth it !
I sometimes get tired, but it's all worth it to see my dear son with his children, enjoying life . My son tells me every day that he loves and appreciates me !