Yes it is but it means the opposite of what most people think it does – that family ties are stronger than other ties. The actual meaning though, is that the blood of the oath is thicker than water of the womb – in other words, an oath tie (at least a blood oath) is stronger than relationship by accident of birth. I can verify this through personal experience. My sister’s (or as I fondly refer to her, my ex-sister) has no loyalty to the family. She opposes us on everything, especially religion and politics, and is always anxious to point out how “wrong” we are about, well, just about everything. Then at the slightest little push-back starts ranting about how we’re all “personally attacking” her, “don’t respect” her, and how she feels alienated from the rest of the family.
Guess what bitch? You are. When you walk away from kin, openly mock the values you were raised with and attack family members for defending those values, you ARE alienated from your family. When you tell your own (former) brother that most of the reason for any success he’s achieved in life is due to his “white privilege,” you ARE alienated from the family. And guess what? YOU are the cause of the alienation. As far as I’m concerned you are no longer kin. We didn’t alienate you, you removed yourself by your thoughts, words, and deeds. Hence EX-sister.