Next of Kin stopping me determining why my brother died

I hope you can offer me some advice.

My twin problem died in hospital recently (not COVID), and I was not allowed to see him before he died - Only Next of Kin and one other.

I would like to know why my brother died, what happened on the day etc.

The next of kin is not talking , and will not cooperate with PALS (Patient Relations) to give them authority to talk to me.

If the Next Of Kin continues to block me, what can I do ?

Regards,

A T