As uk passport holders you will get a 60 day visa exempt stamp (not a visa on arrival) and yes you will be able to extend for 30 days at a local immigration office when in thailand, you can exit and when re entering at the discretion of the thai immigration officer stamp you in for another 60 days + 30 extension. Typically when flying out of the uk the airline will more than likely as for your return flight or an onward flight within the first 60days, it is also possible thai immigration will ask when you enter thailand. You could if you know you dates for leaving and re entering apply for 6 month multi entry visa in the uk which will allow you to come and go within the 6 month period
you get 60 days visa exempt, it changed from 30 to 60 in July 2024, you can then extend by 30 days at immigration inside thailand if you want to stay longer
You can own a house in your name but you will need to lease the land. You can get a 30 year lease on the land anything more than that is upto the lease owner. If they don't give you an extension then you loose the house.
are you sure your not getting confused with the TM7? Which you can get from your local immigration office or online? The TM6 has not been available or required at airports since covid when it was suspended
the TM6 will only be implemented on the 1st of May as it currently stands. If you arrive in thailand before that date you do nothing, no change, no TM6