And is it true that just feed them pellets and give the seeds as a treat ? i saw that in youtube
Different people have different opinions on diet, but... most say:
You should have a mix of seeds, pellets, and fresh fruits and vegetables. Treats can include millet and sunflower seeds (for the sunflower seeds, a bird should only have five or six a day at most).
If you want percentages, it'd be something like...
At the MOST, 2% grapes and heavy starches (potatoes, bread).
2-4% plant powders.
Some owners choose to give their lovebirds protein (eggs, meat), and if you choose to, that should make up 5-10%.
5-10% should be legumes and grains.
5-10% should be fruits like bananas and apples (no seeds).
10-15% should be berries (strawberries, raspberries, etc.).
5-10% can be nuts.
10-15% should be sprouted seeds & grains.
10-15% should be vegetables like cucumbers.
15-25% should be the darker and leafy greens.
This is the IDEAL outline, but since you and your lovebirds are still sort of adjusting, you can probably have them on seeds, pellets, fresh veggies/fruits, and the occasional treat. Try to get them to expand their palates eventually though.