If I have 2 pens and I want to say all of them are green, I can say "Both of them are green" but if I have 3 pens should I use "Triple of them are green" or "All of them are green"?
You could go with any of the following:
All 3 of my pens are green,
All (of) my 3 pens are green,
My 3 pens are all green,
The word triple as an adjective means that the three are parts of one greater object, as seen in the phrase,
a triple murder. Here, there is one case made up of three parts.
It can also be used as a verb to mean 'multiply by three': triple it and then add 4 (n x 3 + 4)
Hope that helps.
You can say "all my 3 pens are green" to mention the number of your pens and their color, simultaneously.