So, after finally being home, and considering the choices, I figured I'd make this as easy as possible for you guys, so this is what I'll do.
Attached here is a file with the character save blocks for both Berkut and Fernand, using the Robin save block from the OP post as a base, so just follow the instructions OP has listed for adding the amiibos, except this time you're adding Berkut and Fernand.
Do also note that they will not have any written dialogue enabled, stuff like lv up quotes, death quotes, etc, will be missing, because those are coded for a certain version of Fernand and Berkut that simply do not exist in the game, so the refferences need to be redirected for them to work, attached here is an example edit to re-enable lv up quotes and class change quotes for English versions of the game, the download also includes a luma folder, just place that in the root of your SD and enbale luma game patching, and USA versions of the game will have level up quotes and class changing quotes for both of them.
Small video of these units in action
Really appreciate this! THanks!