Are Tai-chi and/or Yoga considered martial arts (along with Karate, Taekwondo, Kung Fu, Jujitsu, etc.)?

Yoga is health and wellness. Tai Chi is a martial art. I thas been considered a soft style, but it is also considered by those who know a very effective style once learned. Many people would unnderestimate it and be defeated.

yoga no, however i know people (mainly women) who take it to increase thier flexibility for martial arts.

tai-chi has a negative rep as an "old man in the park" style not a martial art.

however, there are a select small number of teachers that teach it as a martial art- and a smaller number of those that can actually teach or use it effectively as a martial art.

FYI- you get many people that don't consider taekwondo a martial art depending on how its been trained.

basically what is or is not is not dependant on the style's name- its dependant upon if you are learning it to fight and learning to apply it as a fighting system.

XMA for example or tae bo (same category as xma) might pretend to be martial arts, and use the name, but they have little to nothing to do with actual self-defence or fighting.

Tai Chi Chuan is a very effective form of self-defense. Don't let the slow motion movements performed by the elderly in the parks fool you, Tai Chi is deadly. See the Jet Li movie: THE TAI CHI MASTER (1993) to show how Tai Chi is used in actual combat.

Yoga has never been considered a martial art, though most of the Asian martial arts have incorporated Yoga like breathing/meditation within their fighting forms.

yes
Mainstream?... maybe not.
The roots of Yoga are martial, most don't realize this.

Do people seriously think that when the villages of the Tai Chi and Yoga practitioners were invaded the defenders stopped to meditate?
They survived by butchering their foes.

tai chi yes
yoga no

tai chi contrary to the way its taught is a is very good as a self defense art, the problem is very few teach it as this and you get the water down health version instead.