Brynjulf Bengtsson [lejon]

[M.Sjöström]

It has appeared to me that there possibly is no direct attestation that Brynjulf Bengtsson [lejon], grandfather of the Duke Bengt, actually were a child of lagman Bengt Hafridsson. Is this correct? Or, does anyone know of any direct, near-contemporary source to attest explicitly to that filiation (Brynjulf Bengtsson being son of Bengt Hafridsson and not some other Bengt)?
 
It seems that the said filiation as idea is now something like a century old, proposed in an article of Karl Henrik Karlsson. But that Brynjulf's father was in earlier myth-genealogies totally other. This fact speaks for that Brynjulf's father is basically unattested in real sources.
 
Rather than them being father and son, they and their relevant, attested years make them look like contemporaries, of the same generation, to me. If and when they were relatives, they could have been brothers-in-law or something like.
 
Because Brynjulf's attested wife, Ingegerd Svantepolksdotter, must have been born in 1260s at latest (it comes from her mother Benedicta, bc 1225-30, not being in childbearing age later than 1260s, even if had she survived the year 1262), and her first husband Brynjulf customarily would not have younger than her, Brynjulf was probably born in c 1260 (or even earlier). Such date of birth fits with the fact that he died in or before 1315.
 
Bengt Hafridsson's attested children (remember that Brynjulf was NOT an attested child of his) lived so late (something like around mid-14th century) and he himself was lagman both after and before the year 1300. This all makes me think Bengt Hafridsson were himself born in c 1260, too.
 
Onomastics: the names of Brynjulf and his second son Algot, suggest descent from the extensive house of [griphuvud], semi-hereditary lagmans of Westrogothia.
Whereas names of Brynjulf's other children (Birgitta, Katarina, Knut) obviously come from Ingegerd's forebears: Knut from Svantepolk's paternal lineage, Birgitta from Birgitta Haraldsdottir of Norway, Sune Folkason's probable grandmother,  and Katarina from Benedikta Sunadotter's elder sister the queen Catherine. Even the name Bengta Algotsdotter, a presumed granddaughter of Brynjulf and Ingegerd, comes from Benedikta Sunadotter.
The estimated time of Brynjulf's birth would easily fit with him being sister's son of the lagman Algot III Brynjulfsson. And Brynjulf Bengtsson's own name would easily be explained as customary naming from maternal grandfather. His younger son Algot, in turn, would have received the name of a paternal great-uncle, a name very repetitive in Brynjulf's thus-supposed ancestry.
 
Ramfrid Bengtsdotter, daughter of Bengt Hafridsson, is attested of being kin with Ingegerd Svantepolksdotter's sons and sons-in-law. This fact must then be caused by Ramfrid's mother Margareta being Brynjulf's close relative - such as his sister.