I could possibly add some sunflower seeds to the ration mix in the future, but I feel like neither one of them could use any extra weight, especially Zeppy. She definitely is more robust. I think Coco falls right in the middle and I can feel her spine and hip bones with just a tiny bit of pressure. Zeppy on the other hand, hers are a bit harder to feel. She has always been easy to keep weight on.I have also put sunflower oil or black oil sunflower seeds on the feed. VERY moderate amounts.
If you're worried about your girls getting fat, though, you will want to be careful with those.
Up until about a week ago, they were getting some basic grass/clover mix hay that is harvested where I grew up. It just kinda grows wild, almost like a prairie grass mix. Like nothing is done to cultivate or manage it, it's just grown and cut a couple times a year, plus 2 cups once a day of timothy/alfalfa pellets. They could also graze our overgrowth woods/brush when things were green. They kept a healthy weight easily.