Public Records in Archives and FOIL Requests

We attended the excellent FOIL workshop just offered by WNYLRC and hope you repeat it. Our institution has any number of manuscripts and papers that could be considered Fugitive Records: archival material from government offices, most of which was donated decades before the advent of the NY State Archives and modern public record regulations. Multiple area institutions are probably in the same situation.

We have physical custody (long story) of the papers of a retired congressmember from the area, but we deliberately did not send a Deed of Gift, because we did not want legal responsibility and ownership. We would prefer to return the papers to the congessmember because the collection is just too large for us to responsibly house or process. Negotiations along these lines have not been successful and we have not found another taker for them.

My questions are:

1. Are a congressmember's papers considered public records and subject to FOIL requests? 

2. If we do have the congressmember sign a deed of gift, so that we can weed, discard, and transfer as we see fit, are we liable if someone submits a FOIL request for records that we disposed of?

3. For archival records given to us from government offices almost a hundred years ago, are we obligated to repatriate them?

4. Also, are these archival records donated decades ago subject to FOIL requests?