Wow...a whole lot of people have made a whole lot of assumptions that are just plain wrong.
1. This isn't about my vacation time. The first week they were here I was actually still working and took them to work with me and had to cancel appointments to work from home.
How old are the kids? Why could your and DH not get a babysitter?
2. My DH and his ex do not have a decent relationship. They have not been in the same room together in years and s
he chooses to speak with him though me, most of the time. I have a fine relationship with each of them and my ex and I have a wonderful coparenting relationship and live across the street from each other.
He agreed to take the kids because he is afraid to make her upset. But their drama has nothing to do with me.
Why did she not contact you this time? He took the kids because they are his kids.
3. My stepkids are absolutely welcome at my house any time. However, since it is illegal to leave minor children home alone, they are not able to be here whenever they feel like it. (That and the two hour drive between us and their mother's refusal to drive them here. She has never been I our neighbourhood in her life.)
What does the custody order say? Many of the orders I know of, the parent who is getting the kid makes the drive.
4. It wasn't like I would be sitting home and doing nothing all week. I had plans to go out of town to visit my family actually, who I rarely see due to distance.
Without your son? DH could have hired babysitters while he was a work.
5. No I wasn't consulated ahead of time. I was told I had to go pick them up and it was explained to me that his work plans had changed and he would only take Christmas Day and New Years Day off during the 2 weeks. And of course I did it because I love my stepkids.
It seems your DH agreed when he was going to be off and then he could not be off. He did not need to lose his job over this. Our plans changed lots this December, due to DH's job. We had to cancel an out of town trip and I had to pick up lots of the slack. That is what happens sometimes and that is how married people handle the situation as adults.
6. Yes, you bet I expressed my displeasure and we have talked about it several times since. And there will be further discussions.
How many times to you have to beat him up over this? How long have you been married?
7. I would never ever ever leave my son with my DH without asking him first and it has rarely ever happened that he has been alone with him. I wouldn't leave him with his own dad for that matter without making arrangements ahead of time. My DH is not responsible for my son's childcare. His parents are. And do parents really get to go to the grocery store alone?
You never say, "DH, I am running to the grocery store, can you want MY son?" Really!!!! That is what married people do. You seem to have two families that have adults with benefits.
8. My son and his children spend equal amounts of time in our home. Their mother lets them spend every holiday with us because she wants the time to herself. And I am quite happy about having them for those special times and have never complained. I am complaining, not about the holiday, but about all the time surrounding the holidays. We are supposed to share these times, which I think is important for the kids to have time with each family. We had them the entire summer minus a week and a half. So we have them plenty when it is not "our turn" but when you are coparenting from different cities, you do have to take turns. In fact, it's the law here.
This is dictated by the custody order. Custody orders can be altered if both parents agree.
9. The kids and I had fun but they didn't understand why they couldn't spend some time with their mom and commented many times about how they hardly got to see their dad.
I feel sorry for these kids.
10. In our family, step parents are not equal to parents. I am their step mother, not their mother, and there is a different relationship there with different responsibilities. I love them dearly but I would never try to be their mother. And we have all agreed upon this and it works well for us. I have a great relationship with my stepkids. We are very close. That's not the issue here.
11. My husband works to pay child support and his car insurance payment. None of his money supports me, my child or him for that matter. I have a great job and make loads more money. I'm not sure why this is relevant to some people but there you go. And it's not admirable of him to pay child support. It's his responsibility.
So you have the yours and my kids and the yours and my money. 
Where is the marriage?
12. This is mostly not about me taking care of my stepkids or loving them or any of those things. My issue is about disrespect and ungratitude from my DH.
This seems to be a two way street!
13. I firmly believe I deserve to have time off to myself once a year. I work very hard at my job and at being a wonderful mother, stepmother and wife.
Does your DH also deserve this or only you because you so out earn him. 
14. I am not complaining about them being in my home. I am complaining about the expectation that I watch them alone 24/7 for 2 weeks, without a car, to make matters worse.
Why do you not have a car with all the money that you make?
15. Yes, my son enjoyed having his step siblings here. However, he did miss the time that we had scheduled to do things just the two of us and the visit to see his family. I have promised him we will take two days during winter break and go on a trip, just him and I. And, for the record, he loves having time to play by himself. He begs for it in fact and it's rarely ever possible.
Why is it rear for him to have alone time? It appears that you get your son during times when your DH does not get his kids. How many other kids are at your son's father's house? Since you live across the street, couldn't your son just walk across the street to see his dad and get some alone time?
Thank you to those who made an attempt to sympathize or empathize. Your comments were really helpful to me. And you are right about me needing to create more boundaries. I need to start standing up for myself more and stop being used...by both of their parents.
I am shocked at the overt sexism in this thread, and a lot of it has come from women. I guarentee if I was a man the responses would be different.
Not from me. If your DH was off and you had to work, I would expect him to do the childcare, laundry and cooking while you were at work. BTW that is how DH and I do things. We each have one job that we hate and the other person does not mind. Even that job, we would do if the need arose. DH did most of the cooking on his days off this holiday.
This is exactly where my post stemmed from. Thank you! I would have felt a whole lot better if my DH would have recognized that I was being kind to watch the children and that I was doing a good job. And if he would have made an effort to spend some time with them and do something things for us when he was home.
. Either way I'm glad you acknowledge your earlier statement was false and that there is not a court that would rule that a SP isn't allowed to discipline them when they are allowed to be their caregiver.
