apologies for the repost - I have dyslexia and Grammarly sucks...

Previously I have failed a couple of times to secure a second supervisor because I wish to write and illustrate a children's book about visual illusions. When I applied to do a practice-based illustration PhD they said they did not have a second supervisor with knowledge of this subject in the art or any other department including psychology.
So I have now found a uni with experts in visual illusion in their psychology department, but I do not want to study the psychology of illusions on children. I wish to create a book of my own interpretations of visual illusions (for children) on a practice-based PhD.
So I think I should approach the children's creative writing/ illustration supervisor in the art department to find out if I could do a practice-based PhD first.
But I think like the supervisor I approached before he will say it's not his area of expertise and/or interest.
So I'm wondering if I should try it the other way around this time. Should I approach the expert in visual illusions in the psychology department and say I want to do a book about illusions and have him as the 1st supervisor and the children's book expert as the second supervisor.
Is this possible? Or do 1st supervisors have to be in your area of expertise and proposed outcome? (I studied art not psychology for BA&MA)

All I can tell you is that I am officially in Media Studies but my second supervisor is an engineer and most of my modules were taken with engineering and spatial planning students. My PhD is very far over into Sociology yet my Honours is in Creative Media. I think your idea to speak to the visual illusions expert sounds good. Best of luck.