Mt Huashan North Peak by cable car

Well, do you mean that you will only visit the North Peak?
If yes, upon arrival at the North Peak by cable car, you need to walk 3-5 mins to get to the top and then go back to take the cable car to descend. Although the distance is not far, the roads may be still difficult for elder people. So you can just climb a little and appreciate the impressive scenery nearby the cable car.

I have one more question. How far is the North Peak upper station to the Yuntai Mountain Villa at north peak? Is it also via stairs?

Well, I cannot estimate the exact distance. But I remember that you need to walk about 10 mins from the cable car upper station and then arrive at the hotel you mentioned. and yes, there are some stairs. But not too many.