What are the rules regarding taking actions while bluffing?

Question

In Pathfinder, I am in the middle of creating a minor plot element that could become a full-blown side quest where a coven of witches have trained their familiars for the specific purpose of infiltrating settlements as royal guards/soldiers. This as a reference:

As you can probably guess, this completely ludicrous, yet perfectly achievable, ruse requires an insane bluff check in order to work. My question is Would the familiars need to make a bluff check whenever they took an action in order to to keep-up the charade?

Answer 1

Bluff skill works by convincing people that what you say is true:

If you use Bluff to fool someone, with a successful check you convince your opponent that what you are saying is true. Bluff checks are modified depending upon the believability of the lie. The following modifiers are applied to the roll of the creature attempting to tell the lie. Note that some lies are so improbable that it is impossible to convince anyone that they are true (subject to GM discretion). (Source)(emphasis mine)

The bluff roll would be used to stablish a cover, as one cannot expect a unknown person too be readily accepted as part of a community without nobody making inquiries about that person past.

Unfortunately, the scheme you are playing would need more than only the bluff skill, as no familiar, no matter how good liar it is, is going to convince the other guards and the rest of the townspeople that it is one of them unless it looks like one of them (for the reason detailed in the bold part of the quote from above). For that, unless the familiar is going to infiltrate posing as somebody's pet, it will also need a disguise roll (and in most cases, magical assistance):

Your Disguise check result determines how good the disguise is, and it is opposed by other's Perception check results. If you don’t draw any attention to yourself, others do not get to make Perception checks. If you come to the attention of people who are suspicious (such as a guard who is watching commoners walking through a city gate), it can be assumed that such observers are taking 10 on their Perception checks.

Successful Bluff checks effect have not a duration, but their effects can be unmade if the people you fooled have any reason to believe you lied to them. Disguises operate in a similar way, as they work until you do something to attract attention over yourself, which may lead to someone that is perceptive enough to see thorough your disguise. So the familiar would not need to make a bluff (or disguise) check for every action it takes, only for those actions that would compromise its cover in one or another way (by acting out of character for example).

Answer 2

Worry less about the Bluff check and more about the Disguise check

The skill Disguise says

If you don't draw any attention to yourself, others do not get to make Perception checks [to penetrate your disguise]. If you come to the attention of people who are suspicious (such as a guard who is watching commoners walking through a city gate), it can be assumed that such observers are taking 10 on their Perception checks.

A familiar masquerading as a guard and doing guard things isn't being suspicious, so such a creature should have a pretty easy time infiltrating most generic fantasy compounds. The typical mastermind's fantasy fortress offers hordes of nameless guards as living set dressing, so another (disguised) dude in a guard uniform just won't make anyone suspicious so long as the infiltrator doesn't try anything wacky. The familiar need only stay under the radar, using its (and its master's) skills to perform the tasks it's bidden while out of sight of the real guards.

Hence the culture of the assumed fortress matters. A fortress full of militant, affectionate nudists, for example, would be a much more challenging infiltration target for the familiar than the Death Star.

Bear in mind that most familiars are, at their largest, Small (for example, the peacock and the wallaby), so unless the witch or the familiar is capable of some kind of enduring size change magic (perhaps like that which once may have been used on humanity's ultimate infiltrator, Chicken Boo), infiltration of most humanoid settlements will be impossible unless the population is unreasonably and consistently short. (Exceptions for Small races like gnomes and halflings notwithstanding.)

Give the familiar a good story for when the masquerade is blown

The key, then, for a familiar with a poor Bluff skill bonus that's nonetheless used as an infiltrator is to interact with others only enough not to arouse suspicion. With this in mind, the Bluff check should only happen when the familiar is detected as an infiltrator—that is, when the familiar's disguise is penetrated.

As long as the familiar's doing what it's supposed to be doing as per the role it's assumed, there should be no reason to lie. If asked, "Why are you here?" in a place where it's not supposed to be, for example, "I thought I heard something," is a bad lie on the familiar's part, but, "Seeing if the exits are secure," might actually be the truth. It's worthwhile rehearsing such obfuscations before ordering the familiar to commit something dangerous.

The real problem is the higher-end security measures a paranoid mastermind can take. If a dispel magic is cast on everyone entering until each being has no magic on it, or if true seeing is used at every roll call, or if the mastermind employs suspicious experts with absurd Perception skill bonuses, then the familiar may get lucky for a while but eventually must use that Bluff skill. The best option is probably the familiar claiming it's a guard that was magically transformed and forbidden to speak about the event lest the affliction worsen like that crazy witch claimed it would.

Rules suggestion: A witch needs the familiar to prepare spells

A witch needs that familiar a lot. It's not so much the risk of a witch's familiar dying—although that sucks—, but that the witch can't prepare spells until the familiar's return. However, other classes can (more or less) take or leave their familiars. Consider using those classes instead. It still sucks if the familiar dies, but at least the masters aren't also low on spells while the familiar's gone.

Unless the campaign's system-savvy, there's a better option

There's nothing wrong with playing a campaign in which the characters are aware of the rules of their universe and their absurdity. (Webcomics authors in particular take great joy in writing strips about such things.) Unlike D&D 3.5, there's no 10%-either-way rule for Pathfinder's Disguise skill, and turning this into a plot point tells the players not to take the game so seriously. I mean, after all, a snake in Groucho glasses became captain of the guard after a particularly good Disguise skill check.

But if that's not what you're aiming for, familiars will be more successful infiltrating settlements disguised as local wildlife rather than as human-shaped guards. This is both less suspicious and requires less interaction, even though the familiar may still end up an orc's lunch.