Consolidation

I have the following doubts relating to consolidation of accounts:

a) How do we consolidate preference share and prepare C/C account for the same ?

b) How do we consolidate in case there is preferential allotment of shares

c) How is SPL consolidated ?

d) If one of the subsidiary's holds shares in another subsidiary but which is less than 50%, should it be treated as normal investment ?

Thanking in advance