...о конфликте интересов:

Конфликт интересов г-на ХХХ может иметь негативные последствия для Общества, в частности:

в связи с затруднительностью, а в некоторых случаях – невозможностью исполнения г-ном ХХХ своих обязанностей по отношению к Обществу и к YYY одновременно без ущерба для интересов одного из указанных лиц;

...

as (since) it is difficult and, in certain cases, impossible for Mt. XXX to perform his obligations to the Company and YYY at the same time without impairing the interests of any of them..

Благодарю

Rus_Land's 'to fulfill his obligations' (set expression) is better than 'to perform his obligations'. Also 'without detriment to' is good, as it's also a set (legal) expression.

'to the Company and YYY' => 'to the Company and to YYY' is slightly better for a legal document, as it's slightly more formal.

'at the same time' => 'at one and the same time' (set expression) is slightly (5-10%) better here because:

* 'at one and the same time' means 'at the same time as each other'; but

* 'at the same time' could mean 'at the same time as sth else' (a third action).

However, 'at the same time' will be understood.

Nop.

both (of them) - either (of them) - neither (of them)

Three or more people/things:

all (of them) - any (of them) - none (of them)

If you want to specify an exact number, instead of saying 'any (of them)', you can say eg:

'any one* (of them)',

'any two (of them)',

'any seven (of them)' or whatever, as appropriate.

* Note that 'any one' must be two words here; it's not the same as the word 'anyone'.