Paper preservation requires proper storage and safe handling practices. Your family documents will last longer if they are stored in a stable environment, similar to that which we find comfortable for ourselves: 60-70 degrees F; 40-50% relative humidity (RH); with clean air and good circulation. High heat and moisture accelerate the chemical processes that result in embrittlement and discoloration to the paper. Damp environments may also result in mold growth and/or be conducive to pests that might use the documents for food or nesting material. Therefore, the central part of your home provides a safer storage environment than a hot attic or damp basement.
Light is also damaging to paper, especially that which contains high proportions of ultra violet, i.e., fluorescent and natural day light. The effects of light exposure are cumulative and irreversible; they promote chemical degradation in the paper and fade inks. It is not recommended to permanently display valuable documents for this reason. Color photocopies or photographs work well as surrogates.
Family papers should be stored in appropriate sized enclosures, such as a folder, box, portfolio, etc., that will provide physical protection as well as protection from light and dust. The enclosure itself should be made of stable permanent quality materials that will not contribute to the document's deterioration. See Mary Lynn Ritzenthaler's Preservation of Archival Records: Holdings Maintenance at the National Archives for details regarding enclosure specifications, and for easy-to-follow directions on preservation handling procedures for long term storage.