The issues with these photos are not in the post processing. You might be able to doll them up some, but at the end of the day, they will still be merely snapshots.
How much time did you take to study the subject?
How many frames did you shoot?
How many different settings did you try?
How many different PoV's did you take?
How could you have modified the flat lighting?
How would a different time of the day improve these?
The subject matter certainly has potential. You'll need to find a way to draw out that potential. Perhaps if you were to bring a sprayer bottle and spritz the tombstone. Would that create more texture, particularly on the engraved words. Perhaps a reflector to cast more light on it. Perhaps a different prop. My thoughts are that graveyards are best in B&W..... think B&W. Contrast.
Just something for you to chew on for a while.