I'm sorry that your question wasn't answered in a timely manner. We don't have many avian vets on this site. Regretfully, these budgies usually suffer from a bacterial respiratory infection, hypovitaminosis A (lack of vitamin A in the diet), or both. Over the counter antibiotics are not longer available for budgies and so without a vet visit you're necessarily constrained to purchasing a water soluble vitamin such as Oasis brand and hope that the vitamin A in it will correct your budgies' congestion.
Please heat up their environment to 85F by means of a 100W bulb shined into their partially covered cage (not at night when they needs to rest) or by taping a heating pad set on its lowest setting to the sides of their cage. If they appears weakened remove their perches and put their food and water on the bottom of the cage along with them. Add a calcium supplement such as Calcivet or Calciboost to their water along with the liquid vitamin. These supplements are available in pet/feed stores. Avoid over the counter antibiotics designed to be placed in his water. They won't be effective if only because an ill bird won't drink enough to medicate itself properly.
Nutritional imbalances are a common cause of illness in our pet birds. What has their diet consisted of, please? Seeds should compose less than 20% of their diet. A diet of mainly seed and nuts has excessive fat, carbohydrates, and phosphorus; marginal protein; adequate vitamin E, and are deficient in amino acids, calcium, available phosphorus, sodium, manganese, zinc, iron, vitamins A, D3 (necessary for efficient absorption of calcium), K, and B12, riboflavin, pantothenic acid, choline, and available niacin. Ideally, a balanced pelleted diet such as can be found here: www.harrisonsbirdfoods.com or here: www.lafeber.com/pet-birds should be fed as well as hard boiled egg yolk, pancakes and cornbread, the tops of fresh greens, dairy products such as yogurt and cheese, fresh fruits such as apples, pears, melon, kiwi, and berries, vegetables such as broccoli, carrots, beets, asparagus, cabbage, sweet potato, and squash, and even tiny pieces of meat.
Please respond with further questions or concerns if you wish.