"The scriptures state that part of the problem during the time of Noah was that the children were marrying outside the covenant"

I would think the major problem is that the "flood" never happened historically in the first place.  

The second problem with the LDS/Mormon church is that historically the Jews were never slaves in Egypt and therefore would have never learned the Egyptian language.  And even if they did they would have have NEVER used their captors language to write any sacred texts period.

Historically there is absolutely no evidence the Jews were ever slaves in Egypt and therefore would have never learned the Egyptian language. And even if they did they would have have been too proud to EVER use their captors language to write any sacred texts period.

Therefore "Reformed Egyptian" is impossible and the Book of Mormon is a lie.

The Book of Mormon is an anachronism!  "Reformed Egyptian" is fake!  It never existed!  The Jews were NEVER slaves in Egypt.  

There is absolutely NO PROOF that the Jews would ever use the Egyptian language to write on plates that Joseph DIDN'T EVEN USE to dictate the Book of Mormon!  

Even if by some rare chance the Jews were slaves they would be too proud to use the language of their oppressors in any form.