IRA's are not joint in nature (even though we may combine them here, for discussion).
Your RMD is calculated on your holdings; DW does the same on hers, against your respective portfolio's, and age.
Most, if not all companies will calculate your RMD and do the automatic withdrawl for you at year-end (along with taxes due), and most have an RMD tool on their site to give you a heads up on what will be required according to your indivudial age and holdings, based upon your current situation.
As far as your comment on depleting assets, it's not a problem. Just because you are required to start taking withdrawls (and pay taxes) dosen't mean you have to spend the money. You are free to reinvest your "excess RMD's" (e.g. the funds you need to withdraw due to IRS/govenrment rules, beyond what you need to actually spend) and just continue in your normal fashon of investing. However, now you need to consider gains and losses (which I won't go into here).
Heck, if you don't want to bother with reinvestment of excess RMD's, just park them in a CD, if you wish...