In response to the OP, we only have set texts when they get to N5 and H, and even then there is a degree of choice.
Encouraging your children to read widely and broadly, across fiction and non-fiction, and facilitating theatre trips would be the best prep you can give them. A subscription to National Theatre would be a fantastic way to spend some time watching great productions. Reading a poem a week and discussing it as a family also very helpful.
Our BGE goes like this:
S1: greek mythology unit, climate change poetry, a novel unit (teacher and/or class choice), a drama unit, fairytales across the world.
S2: a Midsummer Night's Dream, an intro to media unit, activist poetry, autobiographical writing, a bias/news unit.
S3: a tragedy unit, N4 outcomes, a novel unit, rhetoric and persuasive speeches across history, more literature if we have time.
That should give you some idea of the breadth of what they study.