If you are referring to Crataegus, then yes Hawthorne is edible, the pomes are like tiny apples with two flower spots on the bottom. It is commonly made into jelly, syrups and country wine.
Regarding the seed, you want to pull this out after cooking the pome just like you would the heavy solids of any other fruit. I know you mention raspberry and black berry as examples of some where you don't have to, but it my opinion the seeds ruin the jelly, and I buy and make seedless jellies.
Regarding the toxicity of the seeds, they are roughly as toxic due to cyanide and arsenic as Apple seeds are. You should avoid swallowing too many seeds, but the occasionally missed and swallowed seed is as likely to be as harmful as swallowing the accidental apple seed.