Hi Amjad,
As per your query , you have 4 excel sheets mean, you have to take 4 excel formats as source. You already told that you have common fields across 4 sheets means you can join on the common fields.
You told that you need to generate the full outer join results . Take the all the sources with left outer join and take the all source with right outer join then merge it. Then take distinct of the result gives the full outer join result.
If you give some sample data and required output then I will try to give proposed result.
Thanks & Regards,
Ramana.