To decide how many points of view (POVs) you can handle, you need to take into account the demands a new POV makes on you.
Each POV needs character and voice. When you have more than one or two POVs, then it's important that each one of the characters feels recognizable and distinct, with his own personality and voice that shines through everything they do.
If you don't manage this kind of richness, then multiple POVs draw attention to their sameness or dullness. If you've got good voice for some characters but not others, readers may enjoy some POVs and find others dull, or feel some of the POVs are a distraction from the "real" story.
Every POV needs their own plot arc. It's pretty much assumed that if a character has a POV, that's because their own goals and actions make a plot arc of their own. (It's hard to follow along with a character who doesn't feel like they've got a story, like they've got an arc that's headed somewhere.) So, more POVs means your story is going to be more complicated and multithreaded than one with fewer.
Keeping readers engaged with multiple POVs is harder. The more POVs you have, the longer gap you have between one and the other. Four POVs is likely to mean a four-chapter gap between one POV's chapter, and his next one. That can be hard to follow, or just feel choppy and disjointed. To accomplish this, you need to do really good work weaving the various POVs together, so the reader feels like all the arcs are moving forwards all the time -- or do some other authorial juggling to make the structure work.
In contrast to all these, multiple POVs can be a way to make your story richer, more varied, more colorful. It can make it bigger, with more characters who are truly key and get screentime. It can also let you tell stories with knowledge differences between the characters -- like the examples you give, of B helping A without A's knowledge. or C betraying the others.
These are the considerations you need to weigh against each other. Ultimately, you need to decide whether the added richness is worth the extra complexity, and whether you have enough material to sustain a multi-POV book for its entire length.
Another option that might be appropriate is using omniscient POV -- where you don't have any one POV character, but instead a single omniscient, omnipresent narrator voice, who can dip in and out of all the characters' POVs and knowledge at will. This has its own challenges (particularly, it's not very popular these days), but it effectively lets you skip between POVs constantly, and might be a good solution to the problem you're facing.