i dont know rockets so much but i do know rc plane\heli's
if u want a rocket\veichel to be lifted vertically with 4 ducted fans u'll beed a unique device to stabilize your aircraft
this device call a gyro, u;ll ne more than one in your case and i think this will be hard to do..well not hard but complicated...
imagine that u have 2 controll 4 engines at once togather with you controll surfaces wich will be - ia ssume - the 4 fins of the rocket which will be responsable for the vertical stabilization and for rotate\yaw
no up /down as the rocket do not have any lift if flying vertically->strait line - it should fly very fast to keep it starit and horizental->a speed that i find it hard to belive u'll achive.
there are some rc models that take of verticaly , they are very very lite!! due to nature of their flight pattern.
now that i'm thinking more deeply on the matter, i think that u can use 2 elec motors and to fins\rudders for control which will more easy to setup.
anyway - i hope u will be sucssesfull with this chalenging project
keep us posted