Reclaiming trust income tax - in practice

I have a situation where there a Discretionary Will trust has always been perceived as being in three shares, there are 3 children of the deceased who are the trustees and default beneficiaries and a broad class of other beneficiaries grandchildren etc.

The trust is shortly to receive the income (for the first and only time) from another trust which will be taxable at 45%. Two of the three children have sufficient minors to reclaim all the tax between them but do not wish the benefit of it to be brought into account leaving one share of the trust potentially short changed. The two Trustees would like a three-way split and to reclaim their 1/3 share of the tax but this would leave one beneficiary at an overall financial disadvantage with HMRC retaining some of the otherwise reclaimable tax. There will be sufficient capital to allow for leveling up if needed. No one wants to fall out and there is a letter from the deceased to say all life time gifting is to be brought into account so that overall, each child receives the same, but no one anticipated a tax rebate and I just wondered what is the usual practice is in these situations.

Your proposition seems to be; because Child C has more income that his/her nephews and nieces he/she should get a bigger slice of the cakeā€¦

The question really is do those family elements that have minors keep that benefit for their family, ie 1/3 capital plus 1/3 income plus full/partial tax rebate, which could lead to one side of a family benefiting over all more than another side of the family or is the benefit shared equally ie capital, plus income plus tax rebate divided by 3 giving equality with appointments and distributions adjusted accordingly.