Dear Nikita,
Still I have a lot of corrections: there are a lot of missprints and statements to be corrected.
I have put my comments in the attached text
As for your question, yes, if you want to explain dark matter by the mirror matter, you can make mirror nucleons heavier, but you have the problem of the overproduction of the ordinary helium, if you have symmetric initial conditions.
As for the mass difference of ordinary neutron and protoin, people ascribe it to the violation of isospin symmetry by electromagnetic interaction.
Regards
M.Yu.Khlopov