I don't intend to prolong this discussion; I don't think it is edifying, but I must make two points:
You are being hypocritical. On another thread, you insisted (wrongly) that atonement meant reconciliation and went so far as to try and show what 'atonement' meant in the 15th Century, while blithely ignoring various cntexts that showed that atonement leads to reconciliation but they are not thesame thing.
First of all, you translate the verse as if Jesus were one of several sureties. Does the context lead you to that conclusion? Jesus is Surety (gurantee, guarantor) of a better covenant. True, ἔγγυος is anarthrous, but so is iesus. Is there more than one Jesus?
But the context is not unrelated. The surrounding verses make perfect sense if the Lord Jesus is surety of a better covenant, precisely because, as High Priest forever, He has made one sacrifice of Himself (Hebrews 7:27; cf. 10:12). He has done, as Surety, everything necessary to reconcile us to God, unlike the other priests who had to offer up sacricices continually for thhemseves as well as the people..