Hi Kailaeve1271!
The House Rabbit Society (https://rabbit.org/faq-diet/) recommends 1/2 cup of pellets per 6 lbs. body weigh + 1 cup of greens for 2 lbs of rabbit body weight. As you know, if you want to reduce the amount of pellets they are taking (or even stop feeding them pellets), it’s important to do it slowly, as not to upset their guts. You can start by giving them a bit less pellets and a bit more veggies and see how they adjust, and change the quantities as you see fit. The same site says: “When you feed a lower quantity (or no) of pellets, you must replace the nutritional value without the calories, which is done by increasing the vegetables. Also, a variety of hay must be encouraged all day long, we do this by offering fresh hay a couple of times a day.”
As for the veggies, here is a list of recommended/dangerous vegetables for rabbits: https://rabbit.org/suggested-vegetables-and-fruits-for-a-rabbit-diet/. In my case, I give my bunny 3 types of veggies per day that I rotate according to what I can find in the market.
Unfortunately, I don’t know anything about sunflower oil, but I’m sure somebody else here can help you with that.