Hey, what's wrong sharing a room with a sister? My family was
not well to do (unlike yours staying in a condo) when I was young.
We stayed in a 3 room HDB flat, i.e., two bedrooms too. My parents
stayed in one room. Three of us, my sister, brother and I stayed in
one bedroom. Double deck for me and my brother and my sister slept
on a mattress on the floor.
We stayed together like this until we are married and moved out
on our own.
Of course there is a need to learn how to respect each other
privacy. Other than sleeping, there is nothing much you can do in
the bedroom.
I studied in the living room or kitchen. Anything else you want
to do, you use the toilet...you know what i mean?
Wow. Your situation was exactly identical as mine where my
younger bro and I shared a double-decker whie my 2nd elder sis
slept on a mattress on ground until she went for some
attachment/work overseas last year. The difference is that mine is
a 4-room flat but my 1st elder sis takes up the whole room for
herself. Hope she doesn't stumble upon my post lest she chops my
head off for talking behind her back. 
