Yes, they do, I think.
Consider this case: X, unmarried and childless, makes a will leaving his property Blackacre to his nephews A and B jointly. The Will sais nothing about any other specific asset, or about the residue of X's estate. When X dies, his estate contains Blackacre and a second property Whiteacre. Nobody disclaims anything.
Blackacre passes under the will to A and B in equal shares. Whiteacre passes under the rules of intestacy to whoever is entitled. That might be X's sibling or siblings; if he has no surviving siblings it might be A and B, or it might be A, B along with other nephews and neices. Or whatever — depends on what the family tree looks like.
Right. Suppose A disclaims the bequest of an interest in Blackacre. Blackacre will then go to B alone. What happens to Whiteacre will be unaffected, and A may still get a share in Whiteacre (unless he disclaims that also).
Now suppose A and B both disclaim their interest in Blackacre. The bequest of Blackacre fails entirely, and Blackacre now goes along with Whiteacre to whoever is entitled under the rules on intestacy, which may or may not include A and B. But if A and B would otherwise be among those who inherit from X under the intestacy rules, they won't be excluded on the basis that they disclaimed a bequest.