What is the best visa option for a couple over 50 planning to stay in Thailand for six months each year for two years?

If you find a teaching job, the school can arrange everything for your visa. My school was looking for an English teacher.

Agent can do all hassle free

easiest to do with a multi entry 6-months tourist visa, every other year. Gives you almost 8 months and you only need 6 months. So it is the most perfect and cheapest solution, as there is no mandatory health insurance (which you but should have!) there is no financial proof needed.

It's a no brainer. If you're only doing six months get the METV. No financial criteria.

If you plan to come and go for six months over a two years period and not are comfortable with leaving 800K baht x 2 in a thai bank account for a regular Non O visa and extension of stay in Thailand, you could apply for a one year Non O-A visa. This gives you possibility for to stay for up to two years in Thailand and you apply at the embassy at home with your own bank statement.

The main requirements are the same as the regular Non O visa; -passed 50 years and a monthly income equal to 65K baht or funds equal to 800K baht, but there’s also a mandatory health insurance and health certificate requirement and a regular police check up.

The pro is that you don’t need to transfer any income or funds to a thai bank account. The con is the additional requirements.

The first year the Non O-A has multiple entries, for the second year you’ll need to buy a multiple re-entries permit.

IMO Either metv (multiple entry tourist visa) or OA retirement visa. If you time it right you could get two years out of your OA visa. You do need insurance from goverment approved vendor for that visa though but not a bad thing

The best visa.... by a wide margin, is LTR. If you don't qualify for LTR, Thai Elite is great but very expensive. If not consider annual retirement renewals, but those will come with some headaches.

You started the wrong way round.

Start by finding out, for which kind of visa you can fullfill the terms, and then you know, how long time you actualy can stay in Thailand.

Information about the different kinds of visa, can be found at the website of the Thai Embassy in London.

If you're over than 50 years nothing better than retirement visa

Perhaps a yearly, renewable retirement visa with a multiple entry component.