1. I'm not 100% sure about the lounge but for what I know Premium Economy doesn't entitle to lounge access.
2. If you cancel before 24h to departure you will get all your avios and taxes back, minus a fee of 55$ per person/ticket. See
https://www.britishairways.com/en-be...d-service-fees and also the very useful
Your guide to spending Avios | 2019 edition