Both my wife and I have 1099R forms for IRAs from a participating financial firm. How do I upload the 1099Rs, first using my userid/pwd, and then my wife's userid/pwd?

Yes ... since IRAs have only one owner then each person has their own account so if you use the import function you need to do so for each of you.   It may be faster just the manually key in the form information. 

My question is HOW does one enter userid/pwd for both spouses when using import function?  I am looking for the actual steps I need to follow when using TurboTax.  Note that both spouses have 1099Rs at the same financial institution.

I have never done it  but  the program should walk you thru it ... however I HIGHLY recommend you simply enter the 1099-R forms manually.   https://ttlc.intuit.com/community/entering-importing/help/how-do-i-import-my-1099/00/26254