Nested tuplet ratio notation

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Hello,
I'm testing different ways to notate the top-staff rhythm in the
example below (a 25:16 tuplet over two bars, or a quintuplet built on
four notes of another quintuplet). I have a couple of problems:

1. I'd like to notate the first staff ratio as in the attached image,
but I have no idea how to add a small '5' on top of the eight note.
2. As soon as I add manual beams [ ] in the first staff, the tuplet
number and bracket goes inside the staff, despite the \override
TupletBracket.outside-staff-priorit

Any help is really appreciated!
Lib

\version "2.25.5"

  <<
    \new Staff
    {
      \relative c'
      \repeat unfold 5 {
        \override TupletBracket.outside-staff-priority = #0
        \override TupletNumber.text =
        #(tuplet-number::non-default-fraction-with-notes
          5 (ly:make-duration 3 0) 4 (ly:make-duration 3 0))
        \tuplet 5/4 { \tuplet 5/4 {  c8[ c c c c]  } }
      }
    }
    \new Staff
    {
      \relative c'
      \repeat unfold 4 {
        \tuplet 5/4 { c8 c c c c }
      }
    }
  >>