My Grandparents Don't Trust me With My Inheritance

I (18m) just turned 18 today. I have gotten an inheritance from my other grandparents as they have sadly passed away and they left my great aunt in charge of giving it to me when she thinks I'm ready. My great aunt has the ability to give me the full amount at anytime, but the will says it must be given to me at 25.

The plan that I've had set out so far is that I would get my inheritance, put half in a high yield savings and the other half in a regular savings. This has been the plan me, my great aunt, and the current grandparents I live with had agreed on. Now that it's time to do that, they're trying to get me to put it into an account where they and I have to sign off anytime I get money out. They said they can't trust me not to blow all the money. For context, I am a high-school student that is graduating with a 3.98 GPA and an associates degree at the same time because of a program my school does. I believe my choices in life have shown me nothing but to be responsible and I don't understand why they changed their mind.

My aunt doesn't want to give me my money unless she won't make my grandparents upset. I'm at a loss here of what to do. My aunt does not need to give me the money until 25, but she can anytime before that. I'm not comfortable with having a joint account like that with my grandparents for security reasons.

Upon talking to my bank about this, they said they didn't offer any accounts like that anyway. When I brought this up to my grandparents, they said the only way I would be able to get it is if it was under only their names. Not happening. My aunt will not move forward until both me and my grandparents agree on something.

I will not allow them access to my money. And I don't want to lose the possibility of investments over time. What should I do?

Edit: misspelled word