You do not have to unistall FTM nor reinvite friends for the test.
The test is to see if your problem is related in some way to the computer that you use.
If it syncs correctly on another computer you then know that FTM and your files are OK and you have isolated the problem to your computer.
At the moment you are blaming FTM/Ancestry, which may be correct, but it may not be. You simply don't know.
You need to work through the options and eliminate the variables until you pinpoint the issue.
Both FTM 2012 and FTMM are working and syncing for most people. It is not for you so you need to runs some tests to fnd out why.
There is a free patch coming out for FTMM very soon that incorporates all the sync bug fixes that were added to FTM 2012. Again this may fix your problem.
But with a problem like this you have to work through the options changing one thing at a time.
I would also try syncing with a dummy file to see if it is a file problem.