"each one of them still trusted the other." says that maybe other parts of the family had reasons to distrust each other. Possibly one of the family killed another or was dishonorable in battle. Although the uncle and the nephew get along maybe there was another nephew who had caused problems.

"the threat looming over the thanes as the night approached." Foreshadow for a new danger and a new test for Beowulf. Grendels mother. They had gotten overconfident and many of the people at the party payed for it with their lives.

"She had been forced down after Cain had killed his father's son..." Grendels mother might have been Cain's lover or relative. This sounds like she was alive during that time.

"were grabbed from the bench, many a broad shield lifted and braced.." Grendel's mother appears to be very clever by taking the weapons before she attacks. She will probably be a much tougher enemy than her son.