You can’t owner occupy on two separately deeded properties, selling them together won’t matter. If you like one of them, make your offer and go from there. So you know, 5% down conventional is only for a sfr, multis require 20-15%. Work this out with your lender before you get too far along.
The short answer is no. You will not be able to purchase both as an owner occupied placing 5% down. You could choose one or the other, and be able to do what you are talking about, but once you go over 4 units, it becomes a different story.
Now, that doesn't mean you can't still purchase them with conventional loans. IF they are parceled separately (1 parcel # for the duplex, 1 parcel for the 4-plex), then you can buy 1 of them as an owner occupied placing 5% down (as mentioned above), and then purchasing the other one with a conventional loan and 20-25% down. You can close them simultaneously, or in quick succession, so the Seller shouldn't care if you do it this way, or by 1 loan.
By having them untied, it will give you more flexibilty down the road too, in case you want to sell one and not the other, or refinance one. And as mentioned, the conventional loans will give you more favorable terms and rates than a commercial loan ever will.