Would it help to use an array of columns? So like @kyleheney suggested, create a second column, but you would name the columns ‘Speaker 1’ and ‘Speaker 2’. This will automatically create a virtual ‘Speaker’ column that Glide will see. That virtual column can be used for relations. Just looking quickly, I think this would make sense to do on your Program sheet. This should allow you to create a relation from each individual speaker to each program that they are an individual or paired up speaker. This should also allow a relation from Program to all speakers for that program, whether there are 1 or 2 speakers.
Here another thread where this method was used: