When is a command considered "Suicidal" and when is someone considered an "ally"?

[1Pirate]

Some mind control effects don't allow you to order someone to hurt themselves or grant advantage to the save if they or their allies are attacking the target. However if the perspective of the victim on a course of action is different than that of the controller/charmer, whose viewpoint takes precedence?

I'll use a cambion charm for the first hypothetical.

Charmed person believes a cup of tea contains a lethal dose of poison. The cambion knows the tea is safe, but does NOT know that the charmed person believes the tea is poisoned. He orders the person to drink the tea. Do they get a save?

I'll use Dominate Person for the second hypothetical.

A spellcaster(who the party believes to be an ally) disguises himself and hires a group of bandits to attack and kill the party. The bandits are told to leave the spellcaster alive(but not necessarily unharmed). During the attack, the spellcaster spends one round attacking the bandits(who don't know the spellcaster was the one that hired them), then casts Dominate Person on the party Barbarian(with the purpose of him attacking other members of the party). Does the Barbarian get advantage on the save?

[Aett_Thorn]

In the first case, the player would get a save. THEY believe that the action would be harmful, so they’d get a save. However, if they thought the tea was safe, but the Cambion knew if was poisoned, then they would not get a save.

[Kyutaru]

It's always based on the victim. The victim is the one determining whether the action is harmful because the spell cannot force them to harm themselves. Even if the caster knows it's safe, the victim is freaking out and breaks the charm. Likewise, this is why you actually can cause suicidal actions by having the victim perform an action they believe is safe. "Wait here and don't leave" is a perfectly safe action to the victim even though the caster knows the bomb should be going off any second now.

[Brookshw]

I would also ask myself why a character would believe something is suicidal, whether that belief is reasonable, and if that reasonableness persists based on an altered relation to the caster.

To a cambion and a cup of tea, if the spell creates a friendly or alliance status between the spell victim & cambion then it's very irregular to think the cambion would have offered the victim a cup of poisoned tea without some additional basis for that belief. Its generally unreasonable to think a friend/ally is poisoning you. If the spell doesn't require a reasonableness standard for the belief then anything can be considered a threat/suicidal so I'm imputing one.

[Kane0]

You assume the viewpoint of the target.

[Demonslayer666]

In the first case, it's not obviously suicidal, so I would not consider that a command to commit suicide. I would rule that you would automatically not follow it, and would instead inform your new-found friend why you wouldn't drink it. You would not think they were trying to have you get yourself killed - unless you knew they knew it was poisoned. It's not really a "something is up" thing to warrant a save.

In the second case, no advantage, because the wizard has not attacked the party yet. The first hostile act was casting dominate person, so they were not fighting the party. It's not obvious until that point that the wizard may be on the side of the bandits.