There are two ways to separate your accounts: You can create several accounts in a single data file and customize Quicken to show you just the accounts you want to see at any one time, or you can create separate data files. Unless you have a good reason to create separate data files, creating separate accounts in a single data file is usually the best option.
With a single data file, you can see the relationships between accounts, such as transfers and deposits, and you can see an overview of your finances in one place. If there is any chance that you will ever want to track accounts together, you should create them in a single data file because it isn't possible to merge data files at a later date.
With a single data file, it is also possible to create reports or view net worth measures that exclude certain accounts, like those of a spouse or other family member. To exclude accounts and their transactions from the Account Bar, reports, and the Property & Debt tab, simply customize Quicken to hide the accounts you don't want included at any one time. The accounts will stay hidden until you unhide them.