Problems with receiving inheritance from family

In September 2017 my mother passed away 18 months after my dad, as I've never got on well with my parents or my sister after being kicked out of home at 22 and arguments around my wife and I we had not really spoken with my parents until 2008 when my father's uncle died, this is when I found out that my father had cancer and then started talking we seemed to be getting along ok myself going to see them on my own. So got a call to see the 1st solicitor which I went with my eldest son. We went along to see the 1st solicitor dealing with my mother's estate this is when I found out that my nicece and nephew had a 60/40 split of the estate and my own 2 son's only received £2k each which I wasn't expecting a lot for my son's as they really didn't know my mother. The will was read and my sister got the contents of the house and I got £8k a static caravan or if the caravan had gone £10k and my father's father's war medals which I should have received when I was 25. Then my sister pipes up about a variation in the will that that the grandchildren had been left £10k each to collect at 25 years of age which was to be spoken about at the next meeting as my sister, myself and another were executors of the will. Mr another said that he's would step down which left my sister and myself, then my sister phone's me a week later and asks about the will, probate and changing solicitors as the 1st one was expensive, so to my stupidity I said yes and to save her time so that she didn't have to keep calling me every five minutes that I would let her be sole executor as I also didn't have any access to my mother's estate because my sister had all the keys etc to everything, so this could be completed quickly for all our benefits. After a few weeks I then had to speak to the new solicitor about this variation of the will as I was trying to remove my son's money as didn't want my sister having control over it, this is when she told me that I should get a copy of my mothers father's will and it would explain all. This is when I found out that he had left this £40k for the grandchildren and that it should be put into a trust fund for them all, I then found out that this had not been done and had sat in a bank account that my mother had since he passed away in 2008 now my niece had already received her share as she had already turned 25 which laft 30k plus interest which I wasn't told about and to put the icing on the cake I was left £5k which I didn't receive back in 2008 and that had been sitting in an account so in January 2018 probate was all completed this is when I met up with my sister and she the proceeded to hand me 2 cheques 1 for the £8k my mother left me and the £5k which my grandad left me. I would like someone to help me as I think there is fraud involved here as my sister knew about this money and also I think I should receive the interest on the £5k over the past 10 years (which work's out to be approximately £1.5k) which I've already asked for but got told this is all you get because of inheritance tax. I have also been told that the money that's left is to sit in a trust fund so when my nephew who will be 25 first will get 1 third then my eldest son will then get half and my youngest son receiving the last but from my reading of the will it should have been split into 4 trust funds. Many thanks to whoever's helps me.