@Thomasina79 I am in a similar situation. Eldest son not engaged with any of us for 7 years, only maintains a relationship with his brother (who is disabled and unable to manage his financial affairs).
I have two sons, husband has three children.
Our wills are - all to spouse and then or if we both die together the five children get 20% each. However my oldest son gets one fifth of the 20% with the remaining 4/5ths going to any children he has when they are 25.
We've done this for a couple of reasons. Firstly completely disinheriting gives a risk of a challenge to the Will, but leaving a small legacy means as parents we took into account the estrangement but acknowledge he is still one of us. Equally the grandchildren will receive a sum more than equivalent to what we would have spent at birthdays and Christmas and they will know they were loved and cared for, despite possibly never knowing us.
If you do completely disinherit there is a risk the son who gets everything is pursued by the other two for what they believe to be their share and this could cause him unwanted stress and estrangement from his siblings (if he isn't already).
It's a very personal decision and only you know what you want to do but if you do disinherit, a good solicitor should advise you to do this, but in any event include a letter to each disinherited child explaining your reasons why (helps if it goes to court as there is a clear intent to disinherit).
I should add that our disabled son has no income and lives in accommodation paid for by the local clinical commissioning group and local authority and that situation won't change. As a result of this his money will be put into a trust for him and managed for him appropriately.
I hope this helps. When we give birth we never expect our beautiful babies to grow up and hurt and destroy us do we?