Thank you Doitsu. I manged to get nearly correct epubs through a python script developed by a Burmese professional. The script substitutes the font family and font name from the command line into the css in the script.
I tried the Paduak as well as two other Unicode fonts and they work in ADE reader. I also passed the files to Nook color from the ADE reader and also worked.
When viewing in Sigil or Calibre they do not display correctly. May be this is due to the Qt rendering engine as mentioned in your post. I visited the Qt page and found that this bug was reported in 2010 and it looks like Qt developers are still working on it. I saw there the last post was in July 2012. Therefore the issue is still going on. As Burmese was not a very popular language I suppose the incentive to correct the bug is not so urgent.
Thank you Doitsu for your help.