She and I have a great deal in common–right down to the number of children!
Well, except that. I figure my chances of getting married again are approximately the same as being struck by lightning while being eaten by a shark…
Ah, I see. This is an ambush/trick question.

Gotcha. Well, I"ve been ambushed by far ruder people.
First, let me ask you a question: when you are married in a Catholic ceremony, don’t your wedding vows read “until death do you part?” (or, 'as long as you both shall live" or something?) Well, when your sister married her second husband, so did theirs. So their marriage is precisely like the marriages that you have–that anybody has; until death do they part. So no, as far as ‘heaven’ is concerned, that marriage means nothing more than yours does.
Nothing less, either.
While I will not discuss what happens in the Temple with you or anybody else outside Temple walls (and neither will any other Temple worthy Mormon) I will say this: her first marriage was 'for time and all eternity." Which means that her first marriage will last, if they be worthy, forever. It will be her first husband and she who will be together, we believe. Her second husband is well aware of that, and is well aware that according to our beliefs, he will be with his first wife.
They will enter the Celestial Kingdom together.
I hope this answers your question. I will not discuss the Temple ceremony in any fashion with you, except to mention that it is incredibly rich in symbolism and metaphor, and to take such things as literally as you seem to be doing in your post is to miss a large part of the point.
Yours,
Diana