Can I apply for a 90-day and then a one-year visa for Thailand while in the country?

If you can convert your entry as a tourist Non-O retirement in Thailand or not depends on your nationality and other requirements. But it is a possible way.

You as both 50s or over can have choices

1. Both have Non-O retirement independently - each of you must meet the same requirement separately. Both have to have funds of 800K in a Thai bank account.

2. One gets Non-O retirement and another gets Non-O dependent on a foreigner who is staying in Thailand legally. Only one has to have 800K in Thailand.

The process for 1, take one of these

Both of you can either get Non-O retirement at the embassy/consulate in your country, at a local immigration office in Thailand, or at the embassy/consulate in another country that issues Non-O to foreigners.

For the process for 2, take one of A, B, or C

A. Primary person gets Non-O retirement single entry and another gets Non-O dependent single entry at the embassy/consulate, come to Thailand. Then get yearly extensions together at the local immigration office.

B. Both come to Thailand on Tourist visas (or visa-exempt for the primary person), the primary person applies for in-country NOn-O retirement at the local immigration office, then following 1-year extension. Once the primary person is on a 1-year extension, go to another country for a dependent to apply for Non-O dependent single entry. Enter Thailand again, when a single entry stamp runs out, apply for a 1-year extension (but the same expiry with the primary person) at the local immigration office.

C. Main person applies for Non-O retirement and the second person applies for a Single Entry Tourist visa, then come to Thailand. Same to B after the primary person applies for an in-country 1-year extension.

Maybe a bit more variations but mainly like these.