Considering 1 out of every 1000 children born, have a hearing loss, and you listed a considerable amount of family members with a hearing loss, I believe it is a very safe assumption that the hearing loss is due to genetics.
That said, and not trying to make light of the situation, cochlear implant technology has made great strides.
There are implants that are not yet available that in the US, in my opinion, far exceed the implants available in the US today.
BTW there is a term used for your boy friend, he is called a CODA in the deaf culture. http://en.wikipedia.org/wiki/Child_Of_Deaf_Adult
CODAs usually grow up in a pretty harsh environment. They have a lot of weight on their shoulders placed on them at a very young age. Picture an 8 year old interpreting for his deaf parents via sign, credit card issues, loan details or insurance negotiations... this is just a small example of what CODAs go through.
The truth is, it is some what similar to all first born generations growing up in a country where the dominant langauge is not spoken by the parents. It can be seen in Hispanic and Vietnamese families frequently.
It's an impossible question to answer here for sure. There are many different kinds of hearing loss, some genetic and some sporadic. One would have to know more about the specifics of your boyfriend's parent's situation. Sometimes the history can be very helpful, other times blood tests and scans looking for the more common mutations are needed. It's also frequently not so black-and-white. In other words, your boyfriend may develop hearing problems later on, but never be completely deaf. If it's very important to you both, you might try suggesting to his parent's that they have this worked up so you can make more informed decisions.