First question will be always whether you are a resident for tax purposes. If yes the second question will be whether you are taxed on worldwide or only thai-submitted income. And third question whether your country has a double taxation treaty with Thailand. Has anybody had a proper professional advice yet? When i had it in Indonesia the chap calculated the indonesian tax on worldwide income in line with the self assesment rules, personal allowances and tiered tax brackets as per indonesian tax law, deducted tax paid in UK as per my UK tax return and arrived at the additional tax due in Indonesia. Interestingly the tax liability difference was minimal but headache of the second tax residency can be huge. I decided the world is too big for me to create additional headaches for myself and will simply not stay in any country long enough to become a resident for tax purposes (which usually means more than 182 days in the fiscal year). PS: sending money to your wife is another matter itrelevant to you as it becomes her own tax affair and she may need tax advice.
The max 90 days within any 180 days rule is for European Union Schengen Countries. No such rule for Thailand apart from Thailand no longer likes people living in Thailand on tourist visas including border runs. Same in Mexico post covid and they require people to get proper visas.
…. If you are a tax resident … more than 180 days presence in the country in a fiscal year (Thailand 1st Jan-31st Dec)? Whatever the treatment best not to become a tax resident and divide the year into 3 or more countries… is my moto. The above treatment is certainly correct for Indonesia.