There should be clearly set out what % or share of the aircraft everyone owns. I wouldn't expect it to be expressed as a value though.
I mean I would expect to see that each memember of the group had a 20% share in the aircraft, but I wouldn't expect to see the aircraft valued at 100,000, and each members share being valued at £20,000.
The value of the aircraft will be down to whatever can be achieved on the market at the time of sale.
dp