I recently spent some time at my house in game & noticed my Housecarls never sleep, All they seem to do is eat & sit. Has anyone ever seen them sleep like a regular npc? Or do they just stand,eat and, sit, nothing more?

Unless you mod them or fix them somehow (IDK how, I don't play on PC ), that's all they do. Messed up AI.

When I hear them yawning, I send them to bed.

The ones in Hearthfire occasionally sleep.

I think it depends on their AI and whether or not there is a properly coded and positioned interactive bed in the vicinity. I know Lydia has no access to what should be her bed in the vanilla game. I can't remember other housecarls following a proper schedule of activity either without mods but then it's been a long time since I played without them, and when I played without them I wasn't around the housecarls much because modding is the only thing that makes that bearable.

Probably with UFO and it's sandbox mode. Either that or some mod that fixes their AI packages.