How can my Thai family file the TM30 online, and will we face any fines for the delayed submission?

Is it easy enough for your family to file the tm30 online using the web portal?

That depends on how savy they are with Thai websites, there's a user guide have them read it.

You won't be fined because immigrations has no idea when you left the hotel and actually showed up at that address,.

So have them make a user account, have them add an address, then have them file a tm30 on you and download the receipt.

Just so you understand, you're not going to apply for any marriage visa after this 90 days runs down. You have the 90 day non-o Visa already based on marriage, all you going to be doing is applying for a year extension based on marriage when you have 30 days or less left on your current 90 day entry stamp

You should go to your immigration office, and get the handout listing the requirements to apply for that year extension as far as photos, documents, copies, etc.

Here's the online team 30 website