I assume you inherited this stock from Mom? The question I'd have here given what you've posted is "does the term 'jnt stock' refer to a joint account for you and Mom?"
To directly answer your direct question of "Can i avg the cost of stock from mom death to when (wife and I obtained title)?", the answer is "NO." Inherited stock in almost all cases gets "stepped up" to a cost basis that's the same as the fair market value at the date of death. The tricky issue here is that if Mom put your name on a brokerage account at some point then she "gifted" half of the stock to you when she did that so for that half of the stock her basis became your basis, and didn't get stepped up at her death.
