1- I was at my home playing the guitar, then my dad arrived. (I mean, when he got home I was playing yet). = I was playing the guitar when my dad arrived.

2- I was at my home playing the guitar, but when my dad arrived I was just holding the guitar, not playing, maybe getting a rest. = I was playing the guitar before my dad arrived.

To the first situation, can I use past perfect continuous? - Probably not. I wouldn't use that with the guitar. It would be too long.