It would be sister
I personally never used money orders, I always used personal checks as I wanted to make sure they do not reject the package for any reason.
But through the years of reading here, I’ve read success stories of multiple money orders so you might be okay. So in your case, it would be one money order of $500, one money order of $500, one money order of $440 and another money order for $260. Just make sure the amounts are exact and I would definitely do the $260 separately as USCIS has a new rule that you can’t combine everything into one amount for separate forms.