Welcome, thank you for the opportunity to address your question.
To calculate fair and equitable maintenance in such a co-parenting arrangement, parties need to draw up a list of necessary expenses required by the children (as you have done) as must your spouse. Be sure to be able to support every figure with relevant documentary evidence. You do not rent out your children's rooms whilst they are with their father and therefore you need not pro-rate the accommodation expenses according only to days spent there; include the entire month. Also include all accommodation costs, utilities, house maintenance and repair costs, schooling, transport, clothing, vacation, domestic service, baby sitting and reasonable entertainment costs and any current contributions to tertiary schooling policies if applicable.
Once you have all the relevant costs that both parties are responsible for then the expenses need to be split in relation to the relative income of each parent to calculate the portion each parent is responsible for.
Should the expenses of any parent exceed the amount that parent is responsible for then the difference would be required to be born by the other parent.
Example, H earns R60 and W earns R40. W's expenses in regard to the children are R40 and H's expenses R30. Total cost of maintaining the children R70 split in proportion to the relative incomes ie 40% to W and 60% to H. W would be required to contribute R28 of the maintenance and yet is paying R40, therefore H would need to pay W R12 monthly. Similarly H would be required to contribute R42 to maintenance and yet is only responsible for R30 and therefore would need to pay the balance to W.
Be aware that in some occasions co-parenting arrangements change, often after maintenance orders are final, to the point that one ex-spouse is supporting the children 90% of the time and yet is not being compensated accordingly in the maintenance order.
A maintenance agreement should be as factual and probable as possible as the children are going to have to live on it. A spouse would need to use both his/her earnings and capital to support the children at the standard to which they are accustomed. Do not easily consent to a low counter-offer of a spouse as it means that the living standard and schooling / prospects of the children are similarly reduced.
I trust that I have provided you with suffiecient legal information in order to better understand your position.
There is a provision in the Divorce Act for the loss of patrimonial benefits for substantial misconduct by one spouse, but unfortunately in your case there is no accrual that would be subject to loss.
The accommodation and related expenses of your family have effectively doubled and undoubtedly such increase in costs will impact living standards ultimately. Equally you cannot be required to shoulder maintenance outside of your income and other means and ultimately the size of maintenance may need to be adjusted should your spouse not have any other means from which to support your children eg investments, properties etc. Do not grant leniency just because your spouse earns commission.
In circumstances as this, it would be prudent to approach the issue as the primary residence as chances are that it will turn out that way. Treat any counter offer from your spouse as a reduction in the maintenance budget of your children. If there is no agreement the court will and family advocated are quite skilled at arriving at a fair and equitable position.
I understand this is not the position that you hoped for, but it is important for you to know this to better understand your prospects.
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