Hi Illia,
Thanks for your email. Family members of the jury members are definitely a tricky terrain. If your rules stated that family members of jury members cannot take part, I think it is totally valid to disqualify these images.
So first of all: yes, of course national rules can be more elaborate than the international rules. This is quite common actually - for example, several chapter give out 'Special Awards' or take other national issues in consideration. Conflict of Interest is one of these.
Secondly, what qualifies as a family member, is a cultural question - this is something you should probably consider in the Ukrainian context. I personally definitely would consider it a family member, but I'm not very Ukrainian. It becomes more tricky with nephews etc.
Thirdly you ask if the organizing committee can overrule the jury - now this is a really tricky one. Again there is some cultural background here probably. I'm used to a situation where the jury is considered the neutral body to make final decisions regarding prizes, and nobody would come up with an idea to overrule the jury, unless there are legal reasons or rules that require that. But in another country, it might very well be common to let the jury only be responsible for ranking, and then the organizers make the formal decision. This is something that is probably to be determined by your rules.
I hope this helps.
Best,
Lodewijk