Why is my table value not being called properly?

You're going to have to create a loop and clone the Fire instance multiple times if you want to do this. Also, with how your table is set up, it can be visualized as something like this:

local myArray = { {p1,p2,p3,p4,p5} }

I've demonstrated how to fix both of these issues in the code below:

local part = script.Parent
local fire = Instance.new("Fire")
local db = false

function burn(hit)
	if hit.Parent then
		
		local p1 = hit.Parent:FindFirstChild("Left Arm")
		local p2 = hit.Parent:FindFirstChild("Right Arm")
		local p3 = hit.Parent:FindFirstChild("Left Leg")
		local p4 = hit.Parent:FindFirstChild("Right Leg")
		local p5 = hit.Parent:FindFirstChild("Torso")
		
		local human = hit.Parent:FindFirstChild("Humanoid")
		
		if human and p1 and p2 and p3 and p4 and p5 then
			
			local myArray = {p1, p2, p3, p4, p5}
			
			if not db then
				db = true
				
				for i,v in pairs(myArray) do
					fire:Clone().Parent = v
				end
			end
		end
	end
end

part.Touched:connect(burn)

If you have any more questions or it doesn't work, feel free to ask!