Is my brother being unreasonable or am I?

[EnglishDutch]

Hi I will try to keep it concise! I would appreciate objective views on this.
My dad died in April. Since my mother died 3 years ago, dad vehemently wanted to change his will so the house would stay in the family. My brothers (I have 2) were not interested in the house, I was the only one who wants to live there. It has lots of family history, particularly trees and plants in the garden.
Long story short 1 brother was supportive but the other was not as he felt he would be 'short-changed'. In addition to the house my dad had lots of money and investments. Short-changed brother came up with a spreadsheet which equalised the house so we were all left a percentage (60,20,20) and the investments so they got most of them (grandkids got 5% of investments). At the time the house value was based on estate agents upper valuation. When the will was changed with everyone's agreement, the value to each of us would have been about the same, and my dad was content that the house would stay in the family, as this was the most important thing to him.
Now the house is worth 150k less than on the spreadsheet (RICS valuation) and the investments are worth a lot more than they were then, even after IHT has been paid. I have suggested that the actual figures are put into the spreadsheet and we do a deed of variation to ensure everyone gets the same value, which is what my dad was trying to achieve in the first place. 1 brother is supportive but short change brother wants to leave it as it is. If we do leave it as it is, both brothers will get 90k more than me and I also have to spend money on the house doing things my dad was trying to achieve before he died (so I can live in it). This is quite difficult for me as I am on my own, and don't earn that much.
Am I being unreasonable to want to put the actual figures into the same spreadsheet to get up to date figures? My dad was trying to achieve equity between us, and to make it as easy as possible for me to take on the house and garden. Eldest brother (supportive one) and I do not believe he would have been happy with this degree of disparity between us. Short-change brother's reasoning is that the house is worth more than the RICS valuation (I do not intend to sell the house so I am not sure how we would find out).
I am losing the will to live with it, and I am very disappointed in short-change brother in that he is being very hard-nosed about it, treating is as a business transaction to be negotiated rather than the final wishes of our father, and indeed we were all trying to placate him when my dad (who was terminally ill at the time) put his suggestions into practice (the spreadsheet). With hindsight, we should have found a better method that would allow for market variances, but I was on my knees looking after my dad as well as working full time (I did most of the caring as both brothers were working abroad) and was trying not to upset anyone. Says it all really.
Thank you, in advance, for your replies.

We’ve all lost parents. Most of us manage not to fight with our siblings over the inheritance.

I presume if you hadn't asked that the house stay in the family, then it would be sold and all the estate would have been split into 3 equal shares.
Your dad took into account your wishes and made his will reflect what was fair at the time.
You were happy with the valuation and now you're not.
Too late to move the goalposts now, I'm afraid.

When settling my mother's estate the house was valued by the estate agent which was accepted by HMRC for IHT purposes.

What does the solicitor yo are using say should happen?

I do think you are looking at it the wrong way, you are already better off than you would be 3 years ago.

If your dad died three years ago, you would all have inherited as was intended at the time, based on the house being worth £675k, you would have had to buy your brothers out at £135k each? (would be £105k each now, based on £525k current value) Their investments would have continued to rise in those three years and your house value would have continued to fall, you would also have paid more in inheritance tax.

You (and they) would be in the exact same place you are now, except you would be £60k out of pocket for having to buy them out at the higher rate back then, if you have no plans on selling the house, the value of it is irrelevant, you got what you wanted out of the inheritance negotiation, and you honoured your dads wishes, that's all that matters.

Might be a stupid question but could an actual estate agent value it at more? Then you would poss be 150k up? Without anyone else knowing?