Sibling rates

[Rachael]

I don't give sibling discounts either. Why should I decrease my income level for their financial advantage?

If they go to a gas station and fill up two cars, do they get a discount?
If they go to the grocery store as a family of 5, do they get a discount?

My daily rate is my daily rate and I understand that larger families have larger expenses but it was fully their choice to have a large family and I am not financially obligated to assist them make that affordable.

Would they take a pay cut if you (someone who is a complete stranger at this point) asked them to?
And bear in mind, these reduced fees aren't just a one-off to fill places, it's a loss that you will continue to incur, potentially for years until their children go to school.