Can we replace wheat flour totally with gluten and other grain flour like bhajra, oats etc?
Yes, you can mix gluten and other starch sources to replace bread. The amount of gluten added depends on what type of flour you are trying to approximate. 

All numbers below give the final ratio of gluten. So, "cake flour: 5-6% gluten" means you should mix 5-6 g gluten with 95-54 g of your other flour to get an approximation of cake flour. 

The gluten ratio is roughly: 


cake flour: 5-6% 
pastry flour: 6-8% 
AP flour: 8-11%
bread flour: 12-13% 
high-gluten bread flour (bagel flour): 14-15% 


Flours above that are typically made from durum, not wheat. They are used for certain styles of noodle. 

Note that, if you are using a refined grain starch in addition to the gluten, you will roughly approximate white wheat flour, with slight differences depending on the source of the starch. Tuber starch is also an option, but will absorb different amounts of water. 

But if you are working with whole grain flours of other grains, and not their refined starch, you will have a much different behavior, closer to whole grain wheat flour, and possibly with some other surprises along the way. You will certainly have to test your recipes 4-5 times, fine tuning the water amount at least.