Which flavour of DTV are you thinking of applying? Workcation or soft power? It sounds like on the surface of it, neither. If you really want to apply for the DTV, it sounds like soft power is the way to go. and your partner (needs to be legally married and present a marriage certicate) and son can apply for a dependents visa based on this.

Agreed

There are so many facets to this question - the ability to open a bank account on a DTV, if the thai gov would even try to enforce it. But let's say that it is brought into thailand, and you have stayed in thailand more than 180 days. Technically, it is taxable by the thai government and you technically should do a return. But due to tax treaties between Australia and Thailand to avoid double taxation, this is taken into account in both countries and you as someone has already said end up paying the higher tax of either country.