Winding up of an Estate

In March 2013, my dad had passed away. We launched his will with Sentinal International Trust in September 2013. My brother who is one of the beneficiaries passed away in October 2014. We are unable to get closure on the will because Sentinal now wants to wind up my late brother's estate before they wind up my late father's estate. My late brother did not have a will, however, he has two children aged 23 and 25 years old. Whom according to Sentinal are to benefit my late brother's share from my late father's estate.<br> Please send light as to correct procedural processes. My understanding is that my late dad's estate is to be wound up to finality and thereafter we can finalise my late brother's estate for/to his children.