What's the chance for you to get your mum to travel
between Singapore and Australia (like stay here for up to 3 months)
if she doesn't want to live here for good?
While I understand your good intention of looking after your
mum, you need to learn to let your siblings over in Singapore to
share the responsibility. It makes little difference when you
go home as you'll be working most days.
Please don't get me wrong and I don't mean to sound selfish but
you need to think about your husband too. Once you're
married, you should devote yourself to your husband and your
marriage. It doesn't mean to completely cut your tie with
your family but your marriage and husband should be your
priority.
Instead of just moving back to Singapore for good, you can
always take sometime off to go home to be with your mum.
I hope everything works out for you in the end. I am sure
it'll. Take care!