Welcome sewtired! Congratulations on being the new GM (grandmother) of twins! I'm mom/MIL/ GM, myself and another one who says bravo for being there for your DD and family! I get your feeling "tired and frustrated," however. Most GPs are at least tired after helping their AC (adult children) with household chores or childcare but whew! - I got exhausted just reading about all you do!
So I also agree with those who feel it's time to begin pulling back! And I'm chiming in with those who want to know if DD is sick, in some way, or, maybe suffering from PPD (post-partum depression)? If not, after 6 weeks, IMO, she certainly should be able to begin doing more for herself. Perhaps she's feeling a little overwhelmed, even though another mom might not. So I wouldn't drop out of the picture, altogether. But I agree with those who suggest that you begin to cut back.
I'm a little confused though. You tell us you're at DD's "most of the time" and you've been doing "all the cleaning, laundry and most of the cooking." Yet, the night b4 you posted, DD complained about your "not being there when she needs" you. Chances are, she was just letting off steam b/c she had a rough night with the boys. If so, I would just chalk that up to her own frustration and fatigue and not let it phase me too much. But is it possible that, with all good intentions, you're focusing on the 'wrong" tasks and times of day? Maybe she'd like more help with the babies, even if, say, the laundry slides a little? Or perhaps she feels very alone when DH can't be there at night and would like you to be there, then, more often (I know you are sometimes) instead of so much in the daytime? That might not work for you, I understand, but that may be where her gripe is coming from. And I'm not criticizing you, just feeling around for possibilities.
Then again, it might be a symptom of PPD. Or, of course, part of the syndrome of taking advantage.
As far as SIL is concerned, I'm sorry he doesn't finish what he starts in a timely fashion. I applaud him for wanting to spend time with his DW (dear wife) and new babies but I'm sure he could find time for other things. And DD probably appreciates the time he spends with her and the twins - perhaps he takes over some of their care when he's with them - changing diapers, etc?- but, if so, then she needs to accept that some things, such as the cabinets, won't get done any time soon.
But please rest assured that this is not your problem! Of course, you feel for DD - you're her mom - but she and SIL need to work this out between themselves, just as they will have to work out many other issues together, throughout their lives, as hustband-and-wife and as parents of those 2 boys! It's not your job to step in and solve the problem by fininshing those cabinets, etc. And as a PP said, that probably wouldn't totally resolve the issue - b/c while it might make DD happy, it would very likely antagonize SIL. Also, I trust that you're not voicing complaints, yourself, to either DD or SIL about his not doing the trim in the kitchen or fininshing the cabinets and only expressing these concerns to us. Otherwise, it will just cause tension between you and them.
B/c as GE said, "you cannot make them step up" but you can begin to pull back. If you do, you may be surprised at how quickly SIL gets those cabinets done, etc. But if he and DD decide to let it go, for a while, that's ok, too. The point is that, as you start to remove yourself, not only will you get a break and begin to feel better, but hopefully, DD and SIL will figure things out as a couple.
I'm glad you're away this weekend and getting a chance to spend time with your other AC (adult children) and GC! And I think it's a good sign that DD and SIL are ok with this. Despite DD's complaints the other night, perhaps it shows they're ready to start living more on their own again. Yes!
I notice, though, that you haven't been back in this thread since you posted it. I'm guessing that's b/c you were busy getting ready for your trip, perhaps still helping out at DD's and now, of course, away for the weekend. I hope you're having a great time and look forward to talking with you when you come back in!