I don't know this poster's history, but some of you are being exceptionally harsh. You make it sound like she should give the older kids each their own room BECAUSE they are bonus kids- not because that is what necessarily works in their situation. Otherwise, they will feel displaced by the new baby. Guess what- in all families when a new baby comes along, everyone has to adjust!
I realize she has vented about her situation before, but unless you have ever been a stepmom, you have NO IDEA the storm and strife it creates. (Not to mention that most people I know vent about their families, step or not, sometimes).
When you marry a man with children, there is no way to know the myriad of situations you will be in. Some of them will be great, some of them will not be great- just like any family situation. From what I read of the OP history, she watches her stepchildren all summer with no extra money for fun or activities from her husband, but yet she wants them there because she loves them. I'm sure she has some resentment, but it sounds like she does enjoy the kids and provides for them well (And I never saw her say she intended to put the 13 year old on a couch, only that he wants to do that).
And for all of you criticizing her for calling them her stepkids, just know that might not be all her doing. Just as many of you, especially those of you who are ex-wives, would likely jump all over her if she referred to them as "her kids" because, by golly, she is NOT their mother. In my own situation, my stepsons (bonus kids) get in trouble if they do not refer to me as their stepmom. I get berated (by biomom) if I do not clarify loud and clear that they are my stepchildren. Is that petty of her? Absolutely. Does it hurt her kids who do see me as a Mom? Absolutely. The OP may face a similar situation.