He will get your property (subject to any mortgage) if you leave it in your will to him. Being a long term resident gives him no rights at all.
Whether he will have to pay IHT depends on the value of your property. The current threshold is £325,000 per person. However, that is now transferable. So on your death, I assume you will leave the house to your wife for her life (and vice versa) and on her death she leaves it to your son, there will effectively be a nil rate band of £650,000. So unless your house is worth more than that there should be no IHT.