“My mother and mother-in-law both passed away in 2007. My wife and I donated a lot of their clothing and household items to charities. Can we claim the charitable donations on our taxes if none of our siblings claim the donations? We are filing jointly.”

Did the clothing belong to you? I.e., did you inherit it, or otherwise take possession of it legally and ethically? If so, and if nobody else is going to take it, then yes, you can likely take the deduction, so long as you have a receipt from the charity to substantiate your claim.