Some, like French, Spanish, Italian, and Portuguese, had more in common with one another than they did with, say, German, English, Swedish, Danish, and Dutch, which, in turn, bore only a remote resemblance to Russian and Polish, on the one hand, and the two extant varieties of, say, Gaelic, on the other.
Some, like the romance languages, had more in common with each other than with German, English, Swedish, etc. which in turn only slightly resemble Russian and Polish on the one hand, and the two varieties of Gaelic on the other.