Mom of Twins here....A couple of questions...
Are these your first? That makes a difference. You might be prepared as a mom already and have your routines together.
If this set is your first, are you over the shock of what is
really to come? Even attempting to plan a trip is bold and brave and I commend you for trying to remain in control.
This is a life changing event. It will never be the same!
Is this a family reunion or big family gathering that's not to be missed? Then I say go.
Anything can be done. Whether or not you can recoup after the trip and regroup, handle stress with significant others, deal with inlaws while on the trip is entirely up to you. I think you already know the answer as far as the fatigue and stress level but you really don't want to accept the
change that's going to happen. No one can prepare you until you experience for yourself!
Is it worth it to your two new beautiful children? No, they'll be concentrating on getting new teeth and grasping their bottles. Mickey could be on slide show on their wall for all they care.

They might get very sick on the plane or worse-have ear troubles while fixin' to get their teeth! They can at least swim at six months.
Is this trip for you to "get away" than go yourselves. My husband and I did a weekend away when they were 8wks. They were fine! Go for three days and enjoy, sleep!!
Great to see all the mothers of multiples! I knew you had to be out there!