I have a 3 or 4 gallon fish tank with 8 fish in it is this enough room?

I have 2 Neon tetra 4 black neon tetras and 2 guppies one male one female I am really just wondering if this is enough room i have done this before with 2 zebra fish instead of the 2 guppies and was not successful they all died but one all answers are appreciated and any pointers on how to keep these ones alive...... thanks Kelly