First off do they understand why things are supposed to be done this way. Owners are business people they look at the dollars and see Haccp as an expense taking money directly out of their pocket. If they do not understand why its important then its hard for them to support it.
So maybe do some training with them explain what this haccp stuff is about why its important. give them a dumbed down view of it they don't need to be experts that's your job they just have to understand the "why" behind it.
Look into the MONEY side of things, explain that obviously your customers want all their suppliers to supply safe products, and this is the marketing part where they can say oh ya haccp is great ever since we installed that magnet in product receiving our equipment breakage and down time went from x hours/quarter to z hours/quarter. that continuous improvement is really great stuff.
You can show the owners we had x amount of complaints in these areas if we did these things we can remove those complaints and our customers would do more business, we had x amount of breakdowns, we had x amount of product loss, we had 15 nc's in an audit we failed that cost you 5 grand regardless of failing, if we did this haccp stuff look at all the MONEY you could have saved (or not wasted however they want to look at it".
Hey boss, XL Foods went bankrupt with a zillion dollar recall all because the sanitary welds were not sanitary, that's all it took lets not be those guys.
That's how I go about it, if they are not on board after that, I would start looking for a new job.
Its one thing to have managers/supervisors/ workers not buy in, but when the people who own the company do not believe in what you do especially when food products are made then problems will happen.