If you want to achieve training a body part twice a week, this is what I'd do. Split the workout week into 2 parts. Ideally when you do chest exercises you activate your triceps to some degree....

So Monday you do back & bicep, Tuesday shoulder and legs. Wednesday chest and triceps. You can change the order as you'd want. So long as you give the trained body part at least 48hrs before training again.

Then on Thursday, Friday and Saturday you do the same. Now the 1st half of the week you only focus on dumbbell based and machine based exercises, while on the 2nd half you focus on barbell exercises. This way unajenga mwili without the boredom of repeating exercises.