Hello.
I am a bit confused about some of the points, could you please clarify them, so that I can think of some good solution?
3. A should be replaced with B automatically, when B is out of stock a Pop window should show with ATP window
Maybe you meant the opposite - A to be replaced by B, when A is out of stock. If I misunderstood you, please explain why the business needs to replace and article with an alternative, which is not in stock, despite the fact, that they might have quantities from the original one. It could be that part of the end-to-end process is missing.
4 .Partial inventory splitting should be enabled for VA01 & VA02 when entire quantity is not available for material-A
5. Only B should be displayed in sales Doc( No sub items should be displayed)
So if you have 5 EA of A and 10 EA of B and the customer requests 12, you would like to send 5 EA of A and 7 EA of B, is this correct?
But in this case you need A and B in the outbound delivery, also in the order and billing, because you can in theory have different prices, foreign trade data, materials are used in profitability analysis, they can result in different FI postings and quite a lot of other things, which contradicts the requirement in point 5.
Did you actually mean that you do not wish to print the material codes separately on some internal documents or show them combined on custom reports? Not that it is technically impossible to manipulate the data for printing, but it can be really confusing for employees to handle that and for customers, when they receive a proforma and compare the materials/quantities in it against what they physically receive.