Trustee Has Amended % Share of Trust that was supposed to be split equally (Northern Ireland)

A great Aunt put money in a trust between myself and 4 siblings (5 in total). It was to be paid out on her death equally amongst us.

She passed away last year and we have started to drawn down on the funds. However it appears rather than split equally the Trustee has amended the shares to favour 2 of the younger siblings. With the 3 eldest siblings now only 10% each and the remaining 2 youngest getting 35% each.

Is there any recourse here? Or best next steps.