Put it this way - would your DH be ok with you inviting a houseguest to stay for a few days without consulting him? After all, it's your house and you'd be taking care of your guest... And would he be ok with you repeatedly doing this?
To be honest I think it's a pretty cr!appy father that will happily leave 2 kids that age alone all day watching TV. They are too Young to be left unsupervised for a long period of time.
My SO would not dream of changing the skids' Schedule without asking me first, it's just a matter of courtesy to the other adult that lives in the house (and I love my SD's and get on well with them). Your DH needs to grow a pair and stand up to the BM's emotional blackmail.

As much as I adore my SD3 and would love to have her over absolutely whenever, it would seriously piss me off if BM was changing plans all the damn time!!

Is there a CO?? I reckon it's just best for everyone if the parents stick to the CO!! It's ok to help each other out EVERY NOW AND THEN when planned, and lets be honest, real 'emergency' situations are very few and far between, so there really shouldn't be SOOO many last minute changes!

BM is taking advantage of your DH. Your DH needs to put up boundaries, stick to the agreed times and only take the 'extra' time with plenty of notice and after he's discussed it with you (or 'let you know')

P.S That BM is eff'n lazy!

No way I would be so mad!!! But SO will jump at the chance to have SD any extra time he can get. So he never consults me he just says yes!!! Lucky for me it doesn't happen often :). The one thing I did manage to halt early on was SD calling the shots. She used to call whenever she was "bored" at BM's and SO would high tail it over there to pick her up :O I hated it because it ruined our alone time finally stopped that when he stopped letting her run the show. Now I am pretty lucky because BM uses her as a babysitter for her BF 's kids so she never wants her to go anywhere }:) Works great for me!!

I can see why DH doesn't want to look like he has to check with his boss before he can give an answer every time he has the opportunity to have more time with his children. If the situation were reversed would you feel happy having to ask DH first before telling your ex the children could stay, and saying no I won't have them if your DH refused? How much time are your children in residence with you and DH vs how much time his children spend with you? Because if your children are there 5,6,7 days a week and his only 2 or 3 days a week there would be an argument for saying there is a bit of a double standard going on - it certainly sounds that way when you talk about having a policy that his children cannot stay over on a school night (although it is absolutely dads responsibility to remove electronics and enforce bedtimes). You were annoyed at the lost Sunday afternoon after the dance show, but would you and he actually have had quality time alone? It sounds like you spent the morning with your DD doing what she wanted and he spent the afternoon with his son doing what he wanted.

I wonder if DH is not consulting you because he feels you will say no or make him feel bad about it, so he'd rather have the kids and get into trouble for it later, whereas if he felt that sometimes you would say 'ok thats fine honey' but sometimes say 'i think thats going to be a problem this time because...' he might be more considerate in return. I know avoidance is my husbands favourite strategy.

Having said all this I do understand the frustration in having plans changed at the drop of a hat on a frequent basis. Although I think some flexibility and extra time is good for Dad and children it can be unsettling for all concerned if you can never plan your week or your holiday without changes happening. I would also find it difficult if I was NEVER consulted, because while we have to be considerate of our partners need to spend time with his children he should also be considerate of our right to be kept informed and have a fair input into the schedule in our home.

My DH did this once. Give this example to your DH as a reason WHY you need to be consulted prior.

He agreed to a schedule change with BM without consulting me. Did not even tell me about it.

I get home from work on a Friday, change into something skimpy since it was our 'no kid' weekend. And by skimpy I do mean postage stamps have more square footage. Thick comforter layed out in the middle of the living room floor. Candles lit through the living room. Wine is poured.

Porn is playing on the TV.

And DH walked in with four kids.

If Dad is working 14hrs a day, it makes a huge difference whether he should be automatically agreeing. Obviously if Dad is working those hours it's not Dad who perhaps has to watch over the skids. IMO any time that it is going to be the OP having to do 'the babysitting' , yes, she should be consulted. Having a wife/SO/GF does not mean one gets a on-call 24/7 free babysitter when an ex dumps the kids and DH's a chicken sh*t to say 'sorry, this isn't going to work out for my schedule'.

Also IMO a BM should not e scheduling a date pass 8:30pm on the Wednesday if exchange is 8:30. If she called 'me' and asked can they stay later, I might say yes but it should not be expected and/or demanded. OP's SO has no backbone. Not only with his ex but with his children. Ok, so kids stay, but why the h*ll are they disrupting the household? They can't be playing ipod.ipad and watching movies if Daddy snags items away. If child was to be at my home after 10pm they would be staying until 6:30am the next morning and their pjs would be on at regular bedtime and snoring going on by 10pm.

Last minute changes to the point this BM is making them isn't the type of routine needed changes one thinks of when households occasionally agree to do some extra time or make a few switches. This BM is going above and beyond what should be acceptable. With that said, OP's SO having to say 'wait, BM I have to ask OP first' leaves OP wide open for BM crazy coming right down on OP. That's not right either. IMO Dad as to find the balance somewhere that allows him to have some last minute changes (with Dad doing the child care and implementing household rules and expectations on his kids) or flat out telling BM 'no'. What he should not be doing is speaking for or agreeing for OP if she is the one with the bulk of the 'change' affected.

As far as the weekend skid free couple time, that's really a couple issue and not on the BM or the Skids. If SO is giving up couple time to spend more time with his kids, OP needs to discuss this topic with her SO. Why is SO avoiding couple time or is it just that SO doesn't think of how important it is to a couple to have adult time? Along with that I think SO needs to look at why his ex is calling him to take the 10yr old just because BM can't deal with kid. Why does BM have custody if she can't parent her child on her own by herself when a 10yr acts up? I have to question why it's allowed to relieve BM her parenting duty on nights where her kid won't behave for her. Dad needs to really look at this one. BM can either parent the kid or she can't and if she can't perhaps BM shouldn't have primary.

Nope, no additional time with the skids unless I am consulted first. Period.

My DH would NEVER allow BM to call me a "whore" and if she did, he certainly would not do any babysitting favors for her. (and he would cease all phone correspondece. She would have to email for any request or information she would like to share related to the skids).

You need to pitch a fit about this and your DH needs to decide if he wants a happy wife or a happy ex-wife.

This would be a deal breaker for me. Not only is your DH allowing BM to disrespect you, he, himself is also disrespecting you by not treating you as a partner with regard to his children.