How much pellets does your nethie get a day? I would cut back the pellets to encourage them to eat. Weigh them first so that you can monitor if they are loosing weight.
Hay comes in many different varieties, some rabbits are fussy others are not, some prefer soft hays others harder hays. I have had many rabbits whom I have fostered who prefer a soft hay from a nice bale of hay brought from a farm, rather than the harder types of hay. A bale of farm hay costs around £5, sometimes a little more or often lesss depending on where you live.
If you have a rabbit who does not eat hay experiment with different hay types, there are many hay companies who do sample bags. The hays sold in shrink wrapped bags in many large pet stores and supermarkets are often poor in quality when compared to other hays which can be bought. Do compare them and try new ones to see what your bun likes .
If you find a hay yours likes, you can often mix it with other hays to try and tempt them to eat more.