well its not that complicated they can be used at the same time as well as seprately you see urdu stresses on communicating in two manners one a little formal where we use unhain, app ko , aap and un key ... and when we are a little less formal for example for elders or acquaintances we use aap and its forms "aap ko kahan jana hai", aap ko bura na lagey tou eik baat kahon" these are more in formal context where as mujhey or mujhko is personal pronoun substituing me of english so its more of a matter or personal preference mujhey bhook lagi hai = i am hungry and so is mujh ko bhook lagi hai = i am hungry so they are the same ..... tujhey or tujh ko is used when we are communicating at a very frank level and and they mean the same its a matter of preference for you to choose e.g., tujhey kahan jana hai = where you have to go & tujh ko kahan jana hai = where you have to go so basically tuhey and tujh ko are same but tujh ko and mujh ko are not considered as verified forms of urdu so prefereed forms are tujhey , mujhey unhain , usay and tumhain ..... only aap ko kahan jana hai can be written as aap kahan ja rahey hain or aap kahan jayein gey .......... and one more thing between aap and tujhey is another form which is intimate less formal that is tumhey so u see aap = for respect/formal/acquaintances tum= casual / for friends tujhey = for the person u r extremely frank with p.s. i hope i sufficed you sufficiently

Mujha, Tujha, Usay, Unhey, Tumhey Mujko, Tujko, Usko, Unko, Tum ko, Aap ko