Audio in classroom for senior citizens

Looking for a solution to improve learning for seniors. 1) About 50% of the senior citizens have hearing issues and most of those wear hearing aids. 2) The room is rectangle and comments on one side of the room are difficult to hear on the other side, and the interaction between participants is important. It's not just a matter of amplification, sometimes word recognition is an issue, so louder is not necessarily better. Most hearing aids are blue tooth capable. All of the people have cell phones and most are iPhones. There are some accessibility features on the iphone that may come into play. It's important for the teacher as well as the participants to hear well. Streaming presentations over TVs are heard fairly well by the participants. Naturally, a low cost solution is best. Thanks