Additionally, the Y chromosome haplogroup R1a of the boys corresponds with the man’s (ind. 3). It is noteworthy that in grave 99 the orientation of the adult individuals follows the established pattern of the CWC, whereas both children clearly deviate from it. It appears that the burial orientation pattern was overruled for each boy to face a parent to express a biological relationship.
[Haak et al. Ancient DNA, Strontium isotopes, and osteological analyses shed light on social and kinship organization of the Later Stone Age.
PNAS doi: 10.1073/pnas.0807592105.]
The R1a result is interesting, but I'd like to see Y-DNA results from many more samples before drawing any firm conclusions. Based on his analysis of physical remains, Roland Menk concluded:
The Corded Ware complex s.l. is biologically heterogeneous. The local groups of the core area (Central Germany, Czechoslovakia, Poland) form a very homogeneous block, issued from the local "Old Europe" substratum and persisting until Aunjetitz at least. This block shows no biological affinities to the Ukrainian Kurgan populations. There is no evidence for physical presence of Kurgan tribes in this area. Indo-Europeanization of Northern Europe could be explained by indirect Kurganization, i.e. by invasion of previously Kurganized neighbor groups.
[Roland Menk. A Synopsis of the Physical Anthropology of the Corded Ware Complex on the Background of the Expansion the Kurgan Cultures. Journal of Indo-European Studies, V. 8 361.]
On the other hand, Coon believed:
On the basis of the physical evidence as well, it is likely that the Corded people came from somewhere north or east of the Black Sea. The fully Neolithic crania from southern Russia which we have just studied include such a type, also seen in the midst of Sergi's Kurgan aggregation. Until better evidence is produced from elsewhere, we are entitled to consider southern Russia the most likely way station from which the Corded people moved westward.
I don't think the place of origin of R1a or the timing of its expansion(s) has been pinned down tightly enough as of yet to allow an R1a lineage in a single family to contribute much to the debate on the biological origins of the Corded people.