Individual beneficiaries are not liable for IHT, the Estate is. In other words the tax bill must be paid before the money is shared anyway, so there is no way your siblings can land you personally with the bill.
I�d be more concerned about checking the wording of the Will. If it specifically says he�ll leave you the house and no alternative then when he sells it there is no house to leave you. End of bequest. There are 2 options here. First, if the Will says house and possessions there�s no need to worry. If it says house only, you�ll need to get Uncle to redo Will or do a Codicil to redefine what he�s leaving the three of you.
The Prophet is correct about the 7 year rule. You should also look into the cost of Nursing Homes and the rules about who pays and what is means tested. The tax bill will be less as his Estate diminishes through paying for Care.
I would suggest that you�re not �Aware of the IHT issues� other than that his Estate is likely to be above the threshold. Now is a good time to do some more research. The IR site is quite good, but Google too.