Pantheon soul capture , upgrade questions

1. can you upgrade the pantheon by capturing more than 1 boss listed under it? like have all 3 upgrades?
2. Can the boss map in question bbe white map.
3. Does the boss map in question have to appear on the atlas i .e the path to it be visible.

I have a t 15 sunken city i want to capture the boss aramala the widow which is to upgrade pantheon
but i have not done any map past t 8.

1 Yep
2 Yep
3 Don't think so, you should be fine as long as you are the map opener (don't forget the bottle).

Thanks