Re your father's medals. Although it might be that the 'service' medals were not 'collected' the DFC would have been presented at an investiture of some sort.
I suspect that somebody, sadly and possibly within the family circle, made off with the medals and sold them. Unfortunately, the DFC did not come named, although they were often named later. From what you say it seems that the medals might have been missing for a long time. I should not actually ask this question but somebody must - did your mother remarry and possibly to somebody with older children? It is surprising what happens.
As to logbooks if your father retained his book post service, it is unlikely to be amongst those still held by the RAF Museum because their examples are mostly acquired and they only retain a certain number.
Would there be any circumstances where your father might have gifted them before his death or did he have (possibly) younger brothers/sisters who could have them?
Old Duffer