what do you mean by not breeding? does won't lift? won't stand still? aren't conceiving?
Have they had litters before? I've heard Hollands can be hard to get going after a break so many people keep their does in production. It took me about a year to get my hollands going well but I had a lot of inexperienced animals.
First check over doe for health, make sure vent shows no sign of disease and she is at a healthy weight, Hollands can be easy keeper and too much fat will keep a doe from conceiving. Make sure buck is good and doesn't have a split penis.
Next check signs of breeding readiness,
judging-a-doe-s-readiness-and-breeding-tips-t9869.html
I table breed because i can make sure a doe is properly covered that way, there are many ways to do it but I put buck and doe on a carpeted table, let them sniff a bit and then gently hold doe down while the buck mounts. Sometimes you need to flip her tail up. Watch to make sure doe lifts and buck finishes. I will let the buck have another go if he seems eager and rebreed an hour later.
Other factors are general health, lack of vitamins like A and E, sterility in the buck, time of year
good luck!