Most half orcs are shunned, but some do manage to make decent lives for themselves. It depends on the region and also the degree of civilization. Hollowfaust, for example, doesn't care too much what you did outside of Hollowfaust. It does care what you do inside it.
Now regarding Slitheren, most sane people aka most people on Ghelspad or have ties to it, wouldn't react too kindly to the prescence of them. More than likely they will kill them on sight, (at least in Vesh), but some might just out right shun them and have very little to do with them. Certainly they'd charge exorberiant amounts for it. Now regarding Half-giants...not sure how common they are, also considering the fact that most giants dislike most humans. That being said, a small percentage COULD exist in very bleak regions, or in the mountains (I favor Titanshomes, Gascars and Keldars), but other than that not much else. Gnolls are far more common in Termana and thus it's not uncommon to see some around Termana. Ghelspad, another matter, but still I doubt they'd be too concerned unless they traveled in the Ukrudan desert where they might be mistaken (at a distance) for Sutak.
Regarding party interactions, they can certainly be strained but if you say have a paladin in the group, and can sense no evil in him/her, I'm sure said paladin won't object. Rangers of course might have difficulties, but again depends on race. Mostly though there will be a lot of distrust among the party, unless there's a firm leader and one that has some belief in rehabilating races or belief in redemption. Or just one that's willing to use what is necessary to achieve party objectives.
I hope that helps.