You can, but they will most likely fight, an probebly mate.
Get a female mouse and male mouse, keep them in the same cage, they are likely to mate or breed if they're alone together.
That depends somewhat on your attitude towards baby mice.
the best mouse to keep for a pet is female fancy mouse
yes! female mice get very lonely it is best to keep them in groups of two or three!
Yes. Generally it is best to keep an adult male mouse by itself because if he is with another male they will fight over territory (sometimes to death) and if he is with a female he will breed with her and you probably don't want babies. I would not recommend keeping female mice alone because there is no reason they can't have a friend. A couple females together will keep each other company... this will keep your mice happy and healthy.
Well, maybe it'll make a merbil?
You can have up to 4 mouse
yes
...not if that companion happens to be a cat. Mice are not terribly social animals but keeping two together will keep them more active. An active mouse is a happy mouse. Keep an eye on them when you first introduce them because either one or the other may feel threatened and attack the other. If you put a male and female together, she will soon have pups--and will become protective and may attack the male.
You should not keep a rat and a mouse on the same cage together, The rat will most likely kill the mouse as that is their natural instinct.
"They will mate but if you keep them in there at the birth then the female will kill the male."
its sad but yes...