Lawfully, If you stay even 1 night at a family place , your family should do the TM30 yes. If you don't need immigration service, then up to you I guess.
But the rule is that any hotel, or head of household is required to do a TM30 for any foreigner residing at their place within 24h
You might get refused extension for that reason yes. I did see it first hand. Cheap option to make sure you're covered. Book a bed in a cheap hostel for a few hundred bahts and they will file the TM30 for you. Fill in the hostel address on your TM7 under place of residence.
but TIT, someone has to pay 😁 he was probably just scammed by the guy from the condo office... Paying him 800 says a lot. The fine being 1600b and not 1300b, I'm pretty sure something is fishy
Yes. Every time you enter the country (unless multiple entry visa, reentry permit)
At each place you stay. If you go for example for a weekend to Pattaya, when coming back to your wife's rental property you should file a new TM30 again. You can do it within a few minutes online. My advice would be to ask your wife to register online on behalf of her landlord if he's ok. TM30's will be necessary for many dealings with immigration such as extensions or certificate of residence.