welcome to the site.
1.Shouldn't they be called black spheres?(holes are in 2D right?)
They are called "holes" because they act like holes, things drop in and disappear. The black is a qualifier that denotes "disappearance" nothing is reflected.
(Holes are 3 dimensional in my universe anyway: a circle in the xy plane and a depth in z.
edit:Looking at the wikipedia illustration I can see what you mean by two dimensional: you are referring to the absorbing surface, which in the cosmic holes is a sphere, but as I said the " hole" illustrates the function:dropping down a hole .)
2.What will happen if black holes collide?(If they can)
As with all collisions you would have to solve the relevant equations and set the boundary conditions to see what will happen. These are the general relativity equations.
3.Will they have the "information" of what they have eaten?
This is not a simple nor a totally solved problem, there was the the so called "information paradox". In general, quantum mechanics and general relativity have not been combined conclusively, though there are theories that are very promising . quote: "the predominant belief among physicists is that information is preserved", but physics is about data and theories that describe them, not about the beliefs of physicists.
This is a problem one would have to tackle after having had graduate school courses on both general relativity and quantum mechanics and field theory.
4.What's a white hole? (i'm only 16, so sorry if these seem stupid)
A white hole is the opposite of a black hole, stuff comes out and never goes in. If a black hole is like a sink, a white hole is like a source.