Why does the fact family for 81 and 9 have only two number sentences

Because there are only two things you can do with these two " family" members. 81 divided by 9 is 9. 9 times 9 is 81. Strictly speaking, there should be three in the family: 9,9 and 81 9 is the square root of 81. 81 is the 9 squared.

The first one, i believe, would be correct. all the others have one thing in common, and that's that they have repeating numbers. in the second one, x and y have repeating 6's and 3's, and in the third, x and y have repeating 6's as well. in the last one, there are repeating 3's. the first one has no repeating numbers.