as both SS and ida told u , u need to learn basic scripting as what ur asking for is quite easy but takes a while to explain it , i mean no1 can just paste u a script that does everything as u have to put the option to start the quest on an npc/D menu , for each quest u have to give a flag , after when the player goes in the map to kill , u have to put mondie scripts in mapquest to check for the flag and start counting or not the mobs he kills , then for only 5 quests at the same time , u can do a list were the quests add 1 each time u start it and decrese 1 each time u finish it , and when u start one u make a check to see if that number is equal with 5 ( if = then u cant start , if lower then u can start)
as u see only explaining what u should do takes a while , if i put everything on scripts il give u half of envir folder
) , and it will probably not work as everything has to be done useing ur EXACT mobs name/map numbers/flags that are not used for anything else and so on ...