Adding Spouses to Civi Contacts
There are a couple of ways to do this, but here is the one that I prefer.


Decide how you'll name households. CiviCRM household names are arbitrary, so you can so something like "Jane and John Smith" or "Smith Household". Use a spreadsheet function to populate that field in your spreadsheet.
Import the households as households. Include your membership number as External Identifier. Include your new Household Name field.
Create a unique identifier for your individuals as a new field. Use a spreadsheet function to append "A" to the member number on the first spouse and "B" to the member number on the second.  The result would be that you have member number 1234 and individual number 1234A on the one spouse and member 1234 and individual 1234B on the other. On the second spouse, add another field with the individual number of the first spouse.
Import your individuals with numbers ending in A. Include the member number, and import the field as "Household of - External Identifier". Include the new -A number you created as External Identifier.
Import the "B" spouses as individuals. Include the member number to create the household relationship and the -B number as the External Identifier. Finally, include the corresponding -A number as "Spouse of - External Identifier".


The result should be households that have relationships with the individuals and individuals with relationships to each other.