Damage resistance will just reduce the damage you take (if any) by half, and not effect saves. If your racial ability effected saves, it would say that you gain advantage on saves against poison.
There is no poison damage. The ongoing 5 was not poison, it was 'bleeding', but it was part of the on hit effect of the serrated-wing-slash attack and so by missing, it also missed the bleeding effect. So, Ghunril it scot free (well, he still has Poisoned from the breath attack, which gives disadvantage on all rolls).
Yup. Disadvantage only affects actions that make you roll, you can totally 'work around it' by taking actions that don't require rolls (such as Assist).
I should've looked things up before I made blanket rule claims! Feint isn't the combat action you are looking for (it doesn't exist!). What you want is "Help" which lets you grant Advantage to another character's next attack. So, pick the character you are 'helping' and they get Advantage on their next attack this combat.
is their anyone that hasn't taken their turn yet? Can I apply it to someone that has already gone? That seems tricky since they have already rolled their attacks.
if not Ill just take my disadvantaged attack with spear and unarmed strike.