In your Will, you can leave your estate to whoever you choose, in whatever proportion. However, there are legal provisions that allow children who have been benefited less than their siblings to bring a claim against your Will in these circumstances. This is not to dissuade you from leaving your Will in the percentages that you wish to; it is however important to make sure that you have the necessary advice on the potential consequences, and how to address them.
There are other documents that you can prepare alongside your Will that, whilst not preventing the claim in its entirety, can be persuasive if a claim ever proceeded to Court. Taking the time to speak with a professional can be invaluable to ensure that your wishes are properly implemented and disputes minimised after your death.