That is an excellent question, thanks for writing. In general - and given the best circumstances - it is going to take at least a full year to completely get past the loss. Not only are you going through all of the stages of loss (Denial, Anger, Bargaining, Depression, Acceptance), but every anniversary date is going to re-tear the scab off of the emotional wound. You will mourn on the person's birthday, on every major holiday, and on other special dates. Too, things in your world will remind you of them and bring back some of the pain. Often people speak of, "Expecting to see him/her walking around the corner..."
When you compound the problem by multiplying the loss by two, then you have even more of these dates and times to deal with and struggle through. Plus, if you have particular vulnerabilities toward loss - like if you experienced loss as a child, or if you lean toward being depressive or anxious - then you will have an extra hurdle to clear.
Finally, if your social support system is not intact, or if you have additional stressors (like losing a job, being in debt, etc.), then it will take awhile longer.
But in general, allow yourself a year to feel like you have completed a full cycle, and the pain can begin to ease. If it has been longer, then your condition may have bled into a clinical depression, and visiting the professionals is the way to go for comprehensive treatment. If you are satisfied with the response, please hit "Accept." That is the only way I receive credit for my answer. Thanks-