Are you seeding directly in the ground? How do you intend to use your flowers? I start mine in containers and transplant up to four inch containers before planting in the garden,but I am doing mostly perennials. Al

I'm not sure I understand your question. One seed grows one plant. Two seeds don't grow one plant and one seed doesn't grow five plants.

Are you asking how many plants a person should have of each variety? That's entirely up to you.

Or maybe you're asking how far apart you should space each plant? The seed packets will tell you that. Keep in mind, not every seed is going to germinate and the germination rate is different for every plant. If you're direct seeding, plant a few more than you want in the end and thin out the ones that are too close together. If you're starting them indoors, again, plant a few more seeds than the number of plants you want and see how many come up; toss the excess or pot them up and give them away.