This will most likely be my last response but I would like it if you would answer ALL of it.  While I can not provide the answer to your question on Isaiah 13:18 I am sure others here who think you are mistaken about the number raptured can. Also you failed to answer these parts of my response
A)  I refuse to put limitations on God. And that is what saying he would only save children UAA that are children of christians does and this seems along those lines too.
And
B) Just because the have been parallels on some issue in the past doesn't mean all issues have parallels and that it he save 144,000 Jews from the tribulation he must only save 144,000 christians from it too.
 
And furthermore your "theory" smells like the JW's teaching. But lastly to use your "logic" the 144,000 are comprised of 12,000 from each of 12 tribes of Israel so to parallel then 12,000 must be chosen from each of 12 denominations of the church. Care to name them????
 

Paul