If you are filing taxes jointly, only one TradeLog subscription is needed. Trade history for all accounts filed on the same tax return should be kept in the same TradeLog file. This may include joint accounts as well as the individual accounts of you and your spouse. Each account will be in its own account tab and set to the appropriate account type, and you will run the tax reports needed for filing jointly from the ALL ACCOUNTS tab.
TradeLog allows for one taxpayer ID, so if filing jointly you only need to use the primary taxpayer name and taxpayer ID. Please keep in mind that the subscription level is based on the total amount of trade records for all accounts, which will include all of your accounts plus all of your spouse's accounts.