If you've already agreed to 1 week each, then stick to it, have your family keep the door closed when she comes by, tell them that even though they may want to answer and take the kids, not to do it.
Your W has to learn that if you agreed to something and she then gets to change the terms to what she is more comfortable with, she'll do this with everything.
You can say "no thank you, I'll be taking them when it's my week to take them."
"No more discussions on this, you're an adult, make it work somehow and my family is there ONLY to help me, I've already told them that I don't want them assisting you with this."
"If you need help, ask your friends & family (if she has any), otherwise, deal with it - kids are not there only when it's convenient for you. You already get a break when I have them for the week, that's your break. This week is my break, I'll have them next week at the agreed upon time."
"I'm not enabling you anymore."
"Stop contacting me, asking me to change my answer on this, I'm not going to."
