I have some nike shoes with clips and the straps are never tight enough which is really anoying when you're riding on a tandem.

i really appreciate the reply's

Suggest wearing thicker sox or get correct size/width shoes.

It sounds like the shoe might be too wide. I have pretty inexpensive Answer shoes and they get very tight.

Something that might work (never tried it before but the concept makes sense) could be some type of insole or arch support that might take up some space.

If I understand you post, you're using pedals with toe clips, and the straps aren't tight enough to keep you locked into the pedals.
Are you using cleats on the shoes? Toe clips are designed to be used with cleated shoes. Without the cleat you can't get the toe clips tight enough to really pull back on the pedals.