Usually its one plant ,one container. I suppose if you had a super large container like 20 gallons or more .
You can plant as many at a time as you like .Not sure what that means.

Is is possible to plant more than one tomato at a time in one spot

Most tomatoes are large (i.e. broad) plants, unless you prune heavily (some people prune to one stem or two). Obviously, the fewer stems, the less fruit, so the only reason for pruning heavily is lack of space.

If you had two varieties and only had space for one plant, you could plant them in the same hole. They would need more water, fertilizer, etc., and they probably wouldn't be happy. Unless the two varieties had very different fruit, you might have difficulty recognizing which variety you were eating.

Last year I bought a Black Krim seedling. It was actually two plants in one pot; I think I wasn't aware of that when I planted it -- just thought it was one plant with a sucker (one of the terms for a tomato branch) growing from the underground part of the stem (I had other seedlings like that). But when the plant bore two kinds of fruit it was obviously two plants -- and at that point I began giving them extra water and fertilizer. They were crowded and not real happy, and the BK died before the end of the season.

can there be more than one planted in a container

Raybo/rnewste puts two tomato plants in his homemade rectangular Earth-tainers, which have a total growing medium of 24 gallons -- so 12 gallons per plant.

Now if you were growing dwarf varieties, you wouldn't need as much space or as large a container.

So in other words, everything depends on how much room you have, which varieties you're growing, and how large the containers are.

Even big containers, you'd have to heavily prune if they are indeterminates. My 17 gallon is already filled up by my Brandy Boy