sprzedać is perfective, sprzedawać is imperfective. Perfective verbs cannot be used in the Present Tense, because they denote a specific moment in time.
So here 'sprzedajemy' means either that we are going to sell (Present Continous in the future meaning) or that we are... in the process of selling? Like, imagine, we put both our fridges on eBay.
If it was just "sprzedajemy lodówki" I wouldn't have to go into such interpretations as it would just mean that we sell fridges (for a living, probably).
So, the moment that someone actually buys those fridges, we will be able to say "Sprzedaliśmy/Sprzedałyśmy obie lodówki" (We sold both fridges).