Visa application procedure

Hi, my mother died recently, now my dad age 75 is dating a 36 year old Vietnamese factory worker. He wants to keep her permanently in the house with him instead of her weekend and public holiday stays. I understand there is a cooling off period for 3 months after she goes back (as per end of the factory contract) and the cost to sponsor her is only RM608 per year, and also pay for flight and medical checkup. And then God knows how much salary he will give her, when our mother had nothing.

There is a probability that my dad may marry her. We are not in favour of surprises and I am curious to know how he can do this. Please could someone advice me on these questions:

1. If my dad really marries her, is this a cheaper option than getting her as his maid?
2. Can he apply for a spouse visa without a marriage certificate, assuming she has to go back to Vietnam after the factory work contract expires?
3. Or does my dad need to go to Vietnam to marry her, and then bring her back?
4. If he has made a will before marriage, I understand that would be invalid after marriage. And if he dies under this condition, will she get everything?
5. Sorry this may be a stupid question -- is marrying her an easier way to bring her back to Malaysia?

Honestly, it feels like she is after money. They look odd and mis-matched together, but she is making my father happy by whispering sweet nothings and giggling in Malay.

I find it difficult to be happy for my father, I am already nearing age 50!

I am heartbroken that my mother died for nothing. Having said all this, I know it is my father's house and money and whatever he wants to do with his life is his choice. However, reading answers to my questions will help me learn something new. Thanks very much.

from heartbroken daughter