Share investments held as Tenants in Common

My family (2 parents, 4 siblings), hold an account with a stockbroker, which is owned as Tenants in Common. Any tax (income tax on dividends or CGT on share sales) has historically been divided between the six of us and paid via self assessment. My father has managed the account until recently, but I have now assumed the responsibility using Power of Attorney. Two questions arise: 1. should this account be considered a trust and registered with HMRC and if so will there be a penalty for late registration? 2. should tax be paid through a Trust tax return, rather than by individual self assessment? I suspect my father has failed to keep up to date with recent changes here.

Hi,
That is not for HMRC to advise as this is financial advice which we are not authorised to give.
Thank you.