Is my Ghusl valid if while doing my Wudu during Ghusl I joined my 4 fingers to wipe my hair instead of 3 joined fingers whilst wiping my head?
Bismihi ta'ala
You will not be able to do both wudhu' and ghusl simultaneously and at once.
So, you can either do wudhu' before ghusl, or after ghusl.
When you wipe your head during wudhu', you can use four fingers, or three fingers. Both cases are fine.
And Allah knows best.