No, marrying a Thai doesn't give you automatic citizenship. I do think it would give you residency, but I wouldn't advise it as an easy way to stay. For one thing, if you buy a house or start a business, you will have very few hassles, because the businesses will all end up in your wife's name. Stories abound about the guy(s) who came home one day to find his wife had moved her boyfriend in and him out, leaving him with no legal recourse because he'd done things the easy way and put everything in her name.
That still wouldn't solve the problem of your parents having to renew annually, or how your sister and her daughter are going to get residence.
Even the most generous retirement visa on the planet, Panama's, only gives you a permanent visa if the income you use to qualify comes from a government pension. It guarantees renewal of all other retirement visas (the age limit is usually not enforced) for a set number of years, but that's it.
They aren't kicking everyone out, but they are making it more expensive and difficult to stay there. A great many of these expats lived there for years on 30 day entry passes. There was a whole business that takes people to the Myanmar border from Chiang Mai, waits while people exit Thailand, walk across the bridge, enter Myanmar and pay the $10 entry fee, then get exit stamps and walk back across the bridge and re-enter Thailand. I don't know how viable that is now.
None of the people there are insisting on permanent residence as a condition, and if that is important to you, you are pretty much out of luck in most of the countries that will let you live there to begin with. Even if you got permanent residence, the government could take it back.