affidavit of support - eligibility of joint sponsor

[2monkeys 6]

Hello,

 

I know Im getting ahead of myself, but i have a question about affidavit of support. 

 

I think affidavit of support is required for a k1 visa interview (if not definitely for aos). My fiance is planning to leave his current job early next year so when i go for a k1 interview, he may be between jobs and we may need to ask his dad to be a joint sponsor.

 

The problem is my fiance is the only one in the family who is usc. The rest of his family members are on G-4 visa. My understanding is that a joint sponsor is also needs to be usc or green card holder..
 

does that mean his dad cant be a joint sponsor, even if his income is far above the requirement? And im not sure if it makes a difference, but G-4 visa is quite unique in a sense that when his dad retires, he can automatically apply for a green card. 
 

if not, can we ask someone who is not related to my fiance to become a joint sponsor?
 

Thank you so much for your help in advance!!

[Boiler 45,525]

Does not need to be related does need to be a USC or LPR.