Nobody can give you an answer. They are quite strict these days. For peace of mind I'd recommend getting a spouse and dependant DTV each before travelling to Thailand would be a wise move
look at the website relevant to the embassy you will use for your application, many publish their processing times. But be aware there is not a huge difference between coming in visa exempt and coming in on a tourist visa
currently it allows spouse and children only to a maximum of 4. There's a proposal to lift the cap of 4 but I'm not aware of any plans to change the definition of children which means the child must be under 20 and a grandchild wouldn't count. The daughter and her child will need their own visas
/2024 is exempt. So if you saved 20k NZD from your income in 2024 and transferred it to Thailand that income is also assessable for Thai tax. NZ has a DTA with Thailand so you would complete a Thai tax return and in that return you would work out Thai tax payable and also claim a pro rata credit for tax already paid on that income. It's pretty straightforward once you grasp the concept.