There are 183,000 millionaires in Singapore.
There are 5.6 mil people living in Singapore.
So % of millionaires is 3.2%.
So for couples who are both millionaires,
this should be 3.2% x 3.2% = 0.1%.

You are right, couple millionaires are not in top 1% but
top 0.1%! Wow!