Teaching in a foreign country appeals to many retired couples. You get to travel with an added sense of purpose. You can offer support for each other abroad, dampening the shock of immersion in a foreign culture. Many schools prefer couples as teachers because they can share accommodations. Learning about a new culture is also a great way to reconnect as a couple.
If you're going to be teaching English in a country where it's not the native language, you may need a Teaching English as a Foreign Language (TEFL) certificate. If either of you has a college degree in TEFL, you'll find more opportunities. If you speak the local language fluently and have qualifications to teach other subjects like computer science, music or engineering, it will make you even more versatile as a teaching couple.
Teaching opportunities are extremely diverse. You may find yourself teaching school children, college students or business professionals. You can expect to be paid well enough to live comfortably in the country where you work, but the level of pay may not translate into a generous salary back home -- something to think about if you have a mortgage and other expenses. Typical contracts are for the school year; many teachers then move on to other opportunities.