Switching from Physical Swim to Esim

Hi! I hope someone can help.

I am on my grandma's plan and have full access to the account, such as upgrading phones, adding add-ons, paying the bill, etc., and of course, she is the primary account holder. For my birthday in a couple months, I planned on buying an unlocked iPhone 14 from Apple so I could just transfer my physical sim to an esim. Originally, on T-Mobile's website, you just clicked update sim, which I could do, and then it will ask for the IMEI number for both phones you're transferring between without any other information besides that, which I assume, because I could do that, then I wouldn't need my grandma to do it.

Now, with articles surfacing on how T-Mobile has now changed on their website that if you want to update a sim card, you have to contact them and you can't do it online yourself for the time being, there isn't a definite time frame where this will go back to being able to update the sim yourself, which I do understand they are doing this for security reasons to prevent scams and fraud. 

My question is, if I contact T-Mobile, whether through the message center or call center and I tell them I want to switch my physical sim to an esim, are they going to ask me for the primary account holder's information? I assume that I just need to know the phone number that belongs to that sim and the IMEI of the phone I want it switched to but I want to know if its a simple process and doesn't require me to know certain Primary Account holder information since its simply just updating the sim to esim.

I also read that I won't need the primary account holder if I go to T-Mobile and buy a phone in full and as long as I am in 18, which I am over 18, but I don't want to go, expecting to pay full price for a phone and present my I.D and change sims, just for them to tell me I can't do that because I'm not a Primary Account holder, even when I am paying the phone in full, so that is why I am wanting to just buy the phone directly from Apple and update the sim but want to make sure that no extra information is needed besides the phone number and the IMEI number.

I should also mention I am going from an Android that only uses physical sim to an iPhone that only uses a Esim.

Sorry for the influx of information. Thank you!