Co-parenting means that two parents with custody share the care of the child. It does not have to be exactly 50/50.
In the Netherlands, a child has one main residence, where it is registered, even if it stays at a different address (almost) 50 % of the time. Child benefit is paid to the parent at whose address the child is registered. The care regulations will then determine when the child will stay where.
The Dutch Tax and Customs Administration gives the parent where the child is registered a tax credit. If both parents have a job, they can ask the tax authorities for the combination discount.