Singapore Changi Airport Lounge flying BA First Class

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Good evening. We are a couple flying from Changi airport T1 with BA in First with two family members in clubworld. I believe we can access the Quantas lounge, as Quantas is a oneworld member airline but can we access the First Class Quantas lounge? With the usual ‘can bring a guest’ policy too? I’m hoping our family of four can all enter!
It doesn’t list the first class lounge on the one world lounge webpage.

Advice on the best lounge would be amazing. Thank you so much.