Ballemporium Ball

Hi, I’m getting confused by what seems conflicting advice on this forum regarding online selling. I sell on one or two platforms on behalf of family members stuff they bought but no longer or didn’t use like clothing,footwear,books. For instance old magic books on behalf of my mother in law, dresses I haven’t worn ,my husbands worn/unworn trainers , my sons vintage Lego sets..does this come under ‘chattels’ and if under £6k per financial years does not need to be reported to HMRC. I’m not buying to then sell at a profit. It’s just stuff our household didn’t or no longer uses.