As Jan said, check with your CAA. If hire, different rules apply. I've been a share owner in an aircraft since 1990. This is an "equity" group, with 6 equal shares.
In the UK, the minimum is owning 5% of the aircraft.
I see "non-equity" group adverts in the UK, but don't know their legal status.
I do know of an aircraft where the owner sold a few 5% shares, maintaining overall control.