Bigfoot,
As you own a share in the aircraft, why not bring this up at the first upcoming shareholders meeting?
Bringing it up here on PPRuNe doesn't really help since there is no legal requirement for a regular checkout anywhere in the ANO. The only legal requirements are the 90-day rule for carrying passengers and the two-yearly revalidation (by experience or by test). That 21-day or 28-day currency rule is strictly local to your group and it is unlikely that any of us here know the exact wording of your local group rules so we cannot help you squeeze the most leeway out of them.
And bringing it up here might actually be counterproductive, in case other group shareholders are on this forum as well.