Trying to add Arabic Honorific Ligatures in a font

Design
1

Please forgive me I am new to all this, and need help. I am trying to do something that seems very simple, but I think I am getting confused.

I have 2 open source fonts EB Garamond and Scheherazade. For my intended purposes, I use Honorifics Ligatures as part of the EB Garamond font, so I am trying to add them to EB Garamond font. Which is simple in my mind, as it can be just copied and pasted, which I am able to do, by opening both fonts and just copying pasting what I want to EB Garamond font.
What I dont understand is there official way to name them, and how would use them in InDesign and Word etc? Currently they way I do it is, I use a specific symbol in its place, and than just to replace all in the end, but I would for it to be automated, where as I can type something which changes to that or “CMD+” something.
Please forgive me if I am not even asking the right question, or I am not doing the right approach.

2

Where do you copy the shapes from? From another font?

3

yes, from another font correct

4

How is the other font handling the ligatures. I would expect one of two options. Either use OpenType to substitute the ligature from the underlying text. Or to use private use area unicodes.

5

Other font is purely ligatures, it has 12 ligatures and thats all the font is, so you just type a certain letter and the ligature shows up.