I hate to say 'go read other threads on this board' because it sounds a bit like I'm not bothering to write a proper response to you! But the things you describe are so familiar, and I think it will help you to have a long mosey through past threads...you will see that you are not alone. Most of us stepmums can relate, actually.
Also, one thing you will soon notice is that the common theme in these situations is not the stepkids as much as it is the partners - the DPs and DHs who allow these circumstances to spin out of control. You say "They have no respect for our house and furniture, wake up at the crack of dawn, wind up the dogs, help themselves to the fridge/biscuit tin, draw on my table cloth, don't pull the flush, monopolise the TV, have no Ps & Qs, act like our house is theirs, and my boyfriend basically ignores me... But because my boyfriend thinks if he tells them off or instills any discipline, that they won't want to come here and see him, he lets them get away with things."
You're right - these things are upsetting. Some are things you can learn to live with if you decide to go ahead with a relationship and a life with kids in it. Kids will wake up at inconvenient times, kids will be loud and annoying, kids will misbehvae and forget things, and basically your life will not be the same with them there. All of that, you will have to decide if you are prepared to deal with and maybe even eventually find some pleasure in. BUT - some of these things you don't have to accept...you should be able to have reasonable and age-appropriate expectations about the kids' behaviour, respect for your things, a modicum of privacy, etc, etc. You might need some outside help figuring out what those "reasonable, age-appropriate" expectations are, especially if you don't have much experience with kids yourself.
But it sounds from this like your real frustration is that your stepkids are not following any sort of house rules, and your DP is being a "Disney Dad" - afraid to hold the kids to reasonable expectations of behaviour.
I actually can't agree with fuckity, because I think things can change, and I don't think you are the only one who needs to make some changes! Too often, the burden is put on the stepparent to do all the compromising.
Things have changed quite a bit in my case - still loads of issues and some very bad days - but unrecognizable from four years ago. That is only because both me and my DP - and my SCs, too - were able and willing to put a massive amount of effort into implementing changes. My DP was and still is a Disney Dad, but I'd say he is a Disney Dad in recovery.