Reply from Agony Uncle
1. Yes
2. Generally yes but e.g. in Singapore does not override CPF and insurance nomination
3. Yes. No.
4. No. however after change of nationality we may not be able to hold property in its home country. But the beneficiary can still sell the property and obtain the sale proceeds.
5. Estate duty is abolished. Govern law is determined by the place of the probate proceedings.
6. I would require more details to advice further.