If you disclaim a specific bequest, it goes into the residue and is divided to the residuary legatees - this could include you. The Executors could then "Appropriate" the residue equally amongst the residuary legatees by agreement and you could get your 20 acres depending on the values and other benefits. I have just done exactly that.
Next of kin should have nothing to do with it.
But why not take the 40 acres and sell some to pay the tax? Why give up half your inheritance?
In any case, you need to speak to a good solicitor.
regards