No,If one of the engine fails during flight , the yawing 
moment produced by the other engine is more

no, because there will be no sustained stability.and the 
wing cannot hold the engine load at the end of the 
wing.hence the wing could be damaged.

obviously cannot, coz the area of the wing at the tip of 
the wing is small, it cannot sustain the wait of engine and 
it will affect the lift of the aircraft also.

no.we cannot put the engine at wing tip.
because
*due to wing tip vortices the engine suck the air is 
difficult
*at wing tip have smaller area than root so it cannot 
sustain due to the weight of engine .so it will go damage 
or bend

NO, Due to the following reasons
1.  Usually Engine is very heavy, if it is put at the 
cantilever wing tip, the weight/lever arm is more and 
structurally it is not a feasible design.
2.  Aerodynamic characteristics of the A/C and Engines are 
broadly affected. 
3.  In case of Single engine failure, tendency to yaw and 
roll.
4.  Incase of Electrical fuel system malfunction, Providing 
gravity fuel feed to the wingtip engines is complicated.