[Advaita-l] Saraswati is Shiva's sister?

[V Subrahmanian]

Though this question is not directly related to Advaita, yet the saguNa
forms as various deities require some clarity in understanding.

Here is a verse from the mAdhavIya shankara digvijayaH': sarga 10. verse 70

jAnAmi tvAm devi devasya dhAtuH bhAryAm iShTAm aShTamUrteH sagarbhyAm .

vAchAm AdyAm devatAm vishvaguptyai cinmAtrAmapi AttalakShmyAdirUpAm.

After ubhaya bhArati, verily Saraswati, decides to depart to her abode,
satya loka (for mandanamishra and ubhayabhArati are brahmA and saraswati
who have come down to aid the avatAra kArya of Shiva as shankaracharya),
Shankara addresses her thus:

O devi, I know that you are the consort of brahmA and the sister of
Paramashiva, deity of learning and speech, that for the protection of the
world you take incarnation such as Lakshmi etc. and that you are of the
form of Consciousness.

The questions that arise are:  If brahmA is the 'son' of Vishnu as per
popular belief, how is Saraswati the source for Lakshmi who is the consort
of Vishnu? And how is Saraswati the sister of Shiva?  There is a belief
that Parvati is the sister of Vishnu. There is also a vaishnava belief that
Shiva is the son of brahmA.  If Saraswati is Shiva's sister, she has to be
brahmA's daughter too.  There is also a belief that Lakshmi is Shiva's
sister.  And a brother-sister relationship will make both of them offspring
of some other entity.  Then, Vishnu and Shiva will have to be sons of
someone.

Any answers that clarify the above 'riddles' are welcome.

regards
subrahmanian.v