Hi Guys, I have 2 questions

I have an upcoming reservation, LAX-JFK-SJU on Friday night Jan 2023. For LAX-JFK leg I already have RGU on waltlist.
My sister is joining me the trip from JFK-SJU. Same flight. Both tickets are award tickets issiued from my account. We booked 2 separate reservations but has been linked. LAX-JFK-SJU for me, JFK-SJU for her. And I am platinum medallion. My sister is just a basic member.
Question 1:
Am I able to request complementary upgrade for my sister? As of now, I am able to seclet Preferred Seat for her. Not C+ seat
When it comes to the day of departure, will she able to be on the upgrade list?

Question 2:
Due to the miles avaliable on VS, the reture flight I am trying to book SJU-JFK with VS miles on Delta, for 2 of us together. Then JFK-LAX leg I will book separately for myself.
I should have no problem to ask Delta Rep to replace my VS frequent# back to DL, right? I should not lose any of my PM benefit for DL fight book from VS, right? (Well, specificly I mean we can both be on the complementary upgrade list）
SJU-JFK we can choose Friday 8am or Saturday 8am/2pm . Which one is likely less busy? (More chances to updrade)

Thanks for answering in advance.


Updated:

I called Delta Rep 2 times today, being told 2 different answers:

Answer 1: From Delta Singapore Call Center Chinese line
Linked reservations request complementary upgrade only applys to US 48 Continental States. Alaska, Hiwaii, Puerto Rico not included. So the lady says she cannot click the "First Class upgrade request " for my sister.

Answer 2: US Platinum Line in English
Linked reservations request complementary upgrade applys to US domestic flight, Mexico, Canda, Caribbean Sea，Central America. Basically except for long hual international flights. She believes I should able to click the "First Class upgrade request " for my sister. However, she cannot do that as well. She put me on hold for 20 mins, and asked the other department. And came back telling me , that is the IT error, and she cannot do anything at this monent. She suggested me to call back later. Or on my next flight, go the the Skyclub Agent ask them for help.

Totally 2 different answer. I am confused now. Lol.