I have been experimenting with a multiclassed Draconic Bloodline sorcerer (lvl 14) and bard (lvl 6). I have expertise through bard on both persuasion and deception giving them both +12 and then with 20 in charisma giving an additional +5 for a total of +17
But I get a buff from my sorcerer class allowing me to double my proficiency bonus for any charisma rolls involving a dragon. From Draconic Ancestor:
Additionally, whenever you make a Charisma check when interacting with dragons, your proficiency bonus is doubled if it applies to the check.
I have read expertise as, my proficiency bonus doubles becoming +12 (2 x 6), and my understanding that any charisma rolls involving a dragon gives me a +24 ( 2(2 x 6) ), from doubling proficiency and +5 from base stats giving a total of +29.
Am I right in this assumption?