Executor wants definition of "contesting a will"

Asked in Phoenix, AZ - about 3 years

I have been named an executor in my mother's will. She passed away in November, 2009. One proviso in the will is than any beneficiary who contests the will is automatically disqualified from any inheritance contained in the will. I have begun my due dilligence to assemble any and all assets in her estate and part of that process requires me to inquire about the status of bank accounts she held jointly with her grandchildren (who are also named as beneficiaries). The grandchildren refuse to provide bank statements and trust information in their possession making it nearly impossible for me to excute her will. Does such refusal constitute contesting the will and if so can I exclude them from their bequests without taking legal action?