Suggestion, Charm Person and the Dominate Person are the 3 tiers of mind controlling spells.
They key to suggestion is "The suggestion must be worded in such a manner as to make the activity sound reasonable."
I don't think killing your friends is going to be a reasonable request.
Convince your friends to put down their weapons might work so we can talk this out. The victim might then spend the next couple of rounds trying to talk his partners out of fighting instead of attacking anyone.
That depends how your GM defines 'reasonable'.
Does reasonable mean an activity the creature can understand and is capable of performing normally? "Go pretend you are a frog for the rest of the day."
On the opposite end of the scale, I have seen it interpreted to mean something the subject would do anyway if the thought occurred to it. Which basically means the spell does nothing beyond what the words spoken do.
Suggestion is the on the low end compared to dominate and charm person. If a DM allows suggestion to do anything without a 2nd save or the charisma check that charm person has I would just get heighten spell and use suggestion all the time.
The argument in favor of the suggestion was that since it can only make one suggestion per spell that it can exceed the power of a charm spell. I obviously disagreed.
If a lower level spell can trump a higher level spell then why use a higher level spell? You only need one suggestion per spell anyway so that is an invalid argument.
PS:I understand that we agree, just something to send back to your group. What about dominate person? Even that spell give a 2nd save with a +4 bonus.