Generally speaking EC 261/2004 may apply here, but if your question relates to compensation for either delay or denial of boarding, the answer is almost certainly no. Presuming that the first passenger was connecting on a single ticket (not transferring between two tickets), EC 261/2004 will apply as his original departure was from the EU. However, ATC is generally considered an "extraordinary circumstance" and that means no delay compensation. There is no legal support for denial of boarding compensation for departures taking place outside the EU and you have not provided the gate deadline (which would have been printed on the boarding pass). However, the Regulation does provide for a "duty of care" and thus, SU should provide him with hotel and meal vouchers (or he may attempt to claim these back after his return).
As to the second passenger, EC 261/2004 does not apply at all. He apparently landed in time to make the onwards flight but relied on a gate agent's oral statement that the ticket was flexible. The answer here depends on the fare rules which your friend would know. If the ticket was flexible, then it should have been changed by SU with or without a fee. If it was not, then it was not. Your friend's contract with SU makes it clear that agents may not change the fare rules. In any event, EC 261/2004 has no application as to delay, denial of boarding or duty of care (all presuming that somehow your friend did not even attempt to board his ticketed flight).