1) First, if you are directly next to an ally and an enemy engaged in melee and you are weilding a pistol, are you considered to be in melee with the opponent (since you can wield a pistol in melee), and therefore giving your fellow acolyte a +10 bonus to melee to hit said enemy?
Melee range is defined as 3 meters, if your opponent is in melee with another opponent, and you get within that range, then you will have a -20 bonus to hit, unless you have ambidextrous and gunslinger, if you miss, you might just hit our opponent, but that is GM disgression. Now, your fellow acolyte will gain a +10 if your opponent does not have the talent Combat Master. BUT, there is a talent called double team, that gives you an additional +10 if you outnumber an opponent, and +20 if both of you have it. But combat Master nulifies that too, so if your opponent has Combat Master, you get no bonus.
2) What can you sell items for? If you find a las rifle from an enemy and attempt to sell it, how much does it sell for? Are there any hard and fast rules on this?
75% of original price is a rule of thumb many used, but if you have Barther or Trade Merchant you might sell it at a higher price, none of these rules are raw, but it is the most commonly used ones, numbers might differ, but rarely it is at full price.
3) What skill would you use to get a group of bad guys who are threatening you to stand down by appealing them? Is it charm?
Intimidate to scare them
Deceive to trick them
Charm to make them like you
All of these skills can be used, while the RAW says you use Fel for these, if you fluff it correctly, you can use strength, int, or even agility, it's all about the fluff and if your gm allows it, only intimidate can be used with str int and fel according the the book.
4) If you roll on the aquisition chart, the chart that has how hard it is to find something in a given community, and you fail your fellowship roll, when you can you reroll your fellowship to attempt to find said item again? A day? A month?
When you roll on something you are searching for, you know the difficulty and the time, after the time has past, you can look again. It is not that if you fail, you don't have to search, that would be daft.
5) Does a psyker have to use Psyscience to sense the presence of other psykers or psykic pheonemena(sp?)?
Psyscience is an awareness test of the warp, and you can rarely see if a person is a psyker or not, so this skill is the only sure way to identify psykers, with psychic phenomena well, some affects you, others don't, but if a phenomena is happening withing range of the Psykers psyscience awareness, then it will be detected, do remember that in most cases, most characters would not recognice this, unless they have experience with it from the past, or in the background fluff about the character.