As long as you are being happy, productive parents to the child, then it's all good to me. What you describe as "co-parenting" is actually quite normal these days with parenting. Think of the child though.

So you mean you donated sperm to a surrogate mother or you had sex with a woman and she has the kid and y'all have no romantic relationship? And you are conducting this like a business transaction with women or are attempting this with female friends that you know?

Works in theory, until (as in any relationship) the small differences start to accumulate and implode the planned equilibrium.
But it is possible, it all depends on the capacity of the parents to solve problems and help each other.
It becomes easy when there is love, because empathy will be high, and that is probably the evolutionary reason of love.

Very complicated

I have no children, and intend to keep it that way. I don't know whether theists and non-theists, on average, are significantly different in how they co-parent. I'm a volunteer mediator and I've mediated a fair number of parenting plans; although holidays are often discussed, specific religious issues are rarely brought up. I don't know whether anything can be extrapolated from that, however.

What do you agnostics think? I'm not a judge. People have kids and then no longer live together the children still need to spend time with both parents. When this is not allowed their minds are poisoned. The many aspects of people's lives has to be taken into view as well as the best interests of the children.