This is so frustrating, I get that.
I think you are making 2 main mistakes:
1) You are reasoning with a 2 year old and assuming that, because he has the vocabulary, he also has the emotional understanding of what he's agreeing to. He does not. The reasons for him doing what you want need to be from his perspective entirely - not yours. You're just talking way too much - at night, and during the day. It's like kids who say, "Oh, let's get a dog. I promise I'll walk it every day and feed it and do everything." They say it 100 times, whether they are 4 or 8 or 12. They even mean it when they say it. But 2 days after the parents get a dog, it's the parents' dog entirely. That's the nature of children. It's easy to be put off by his verbal abilities. He's still 2. My cousins, BTW, have a 5.5 year old who is also verbal and he's now impossible because they talk him to death and never follow through on stuff. What their mistake is - they don't work on his level.
2) You are giving in. So yes, the whole routine is taking longer because you are changing it every day or every few days. So, he's learning that nagging/crying work perfectly well, and that someone will eventually snuggle with him. You have 3 choices: a) barricade the room with a gate and let him cry it out, knowing you will be miserable; b) keep taking him back to bed, 10 or 20 times if necessary, with no snuggling and no talking beyond one agreed-upon phrase that you and your husband repeat every single time ("It's bed time. Night night" or whatever you choose, but zero variation from this) which will make you all miserable but which will work eventually (in a couple of days) when he sees he's not getting his way; 3) putting a sleeping bag or little cot at your bedside where he may sleep with zero talking besides "Night night" and which will only work if he gets up after you are in bed but not if you are still doing stuff in the main part of the house (eventually, he'll get sick of being on the floor but in the short run he won't be alone).
No matter which method you choose, you will have 3 nights of hell and then it will be done. So pick a weekend and just be miserable Friday/Saturday/Sunday night or whatever, and get through it. And I agree that, if this is going to take 40 minutes instead of 10, you start 40 minutes ahead of the usual time.
I know this is hard to listen to but you will be glad you establish yourself as having house rules that he has to abide by whether he understands them or not. If he knows he's not going to get added attention, he'll eventually stop. If he thinks he can get you to cave, or if he turns everything into a negotiation (one more story, lie down with me, sit by the door, whatever), then he is in charge of bedtime, and that's not going to end well. He needs his rest more than anything, and you have to make it happen.
Whatever you choose, you and your husband have to agree 100% ahead of time and commit to doing the same thing. You need to get this done before the next change of moving the brother into the room.