What exactly defines "family"? Sure sharing DNA gives a commonality between people, but there are those people who fill the role of "family" not because they have to, but because you are drawn to each other for an unknown reason. For whatever reason, you share a deep connection based on an experience, a similar belief, or for some unknown reason that only G-d knows at the time.
Family members can continuously be gained throughout your life. You might not be aware of it occurring, you might not be able to pinpoint the exact date or time, you might be able to, either way it happened.
For example, when you are in 5th grade after moving to a new city and you meet a random 6th grader. Or in college while talking for 30 minutes two days in a row because of the Greek lettering system. While being involved in a religious community that you identify with. When you got married, moved across the United States to a place not knowing anyone and bought a house next door to complete strangers. Or that time you found yourself dealing with a difficult situation and you come home to baked goods randomly sitting on your doorstep. Then there are the people you meet who are in your shoes and while the situation might not be exactly the same, the experience is pretty darn close.
These adopted family members are so special. They have a choice every day whether they will stay in your life and whether they will be active or passive participants. They choose to not write you off when you lose touch for years at a time. They call you up to check in when you've been meaning to do it for weeks on end. They reach out to you when you think no one is there. They bring you coffee and send care packages. They sit and talk for hours on end about topics that can be painful to themselves.
No matter who it's made up of, all family is important and all members are necessary to keep the unit afloat. Us personally, well we happen to have won the lottery a second time when it comes to ours.