Rats need good quality blocks every day - Harlan Teklad 2014 and Oxbow are recommended - the blocks need to be low protein such as 16%, 15% or 14% protein - the blocks provide the nutrition they need
They also need a variety of daily vegs such as baby kale, broccoli, peas (frozen thawed are good), cooked sweet potato, cooked squash, mixed greens, fresh or cooked carrots, cauliflower, a piece of cucumber, a few cooked beans, a few cooked chickpeas, etc
and occasional healthy treats such as a piece of fruit, berries, cooked grain such as oatmeal, cooked quinoa, organic pumpkin seeds, organic kumat puffs etc
They need foods that do not have added sugar, added salt, or added fats.
Ferret kibble is not good for rats as it does not meet their nutritional needs and is likely too high in protein
Avocado has good fats - but the part near the skin as well as the parts near the pit are toxic to rats
Organic pumpkin seeds are also good
You need to buy them rat blocks.
In the short term you can give cooked grains, cooked quinoa, and a wide variety of vegetables and a bit of fruit.
You can also give baby food.
Is the problem that they have been eating a very unhealthy diet, or do they have health issues?
Do they have problems eating food?
How old are they?
Pictures??
hope this helps