If three instanteous velocities are found, how can they be used to draw a velocity vs. time graph?

Answer 1

your question is ambiguous. Do you mean three velocity functions or three points (velocity,time). If the latter, you have three points. If you have any prior knowledge of how the velocity should behave with time, you can fit them with that in mind. If not, a linear fit is as good as any with just 3 points.