I think your feelings are entirely natural. Inheritance issues can cause a lot of problems in families. I am never quite convinced by all the posters who come on to threads like this and say you are grabby and should be pleased for your parent etc.
I think most people would be delighted for their parents to live long and happy lives and to spend all of their money before they go. But when they do go, it's understandable that you would hope to receive your share of the estate which was owned by the predeceasing parent. As one PP said, it's a link to the first parent you lost.
But try not to let it spoil your relationship with your father. As someone above also said, there might not be anything left at the end anyway.
In my case, grabby stepmother tried to poison my DF against me and DB, and caused a rift for a while. He changed his will in her favour and, at her insistence, did not tell me for 3 years (even when he did tell me DF said I wasn't supposed to know and that stepmother had promised to leave everything to me when she died). Before he changed it, he had given her a life interest, which I understood and was happy about, but not happy to be excluded altogether and even more unhappy that it was done secretly, especially as i had a very good relationship with DF.
My brother predeceased my DF after he took an overdose. He was very close to my DM although he and my father never got on. My DF, spurred on by stepmother, had cut all ties with him, so the inheritance was not relevant to him.
I was on very good terms with my DF when he died. He lived a few hundred miles away but had just spent Christmas and New Year with us, and he met my DC regularly, which meant a lot.
There wasn't much left in his estate when he died. He never saved or had a pension, and the flat had a mortgage on it. Stepmother and I got on for a few months after he died, although she was awkward at even letting me have a few bits of family furniture which my DF had said openly on several occasions were to come to me (she even used to joke that she was polishing it for me). She was laughing and joking at the funeral and had moved in another man within 6 months.
I had an interest in the house due to previous financial contribution and I am afraid it took court proceedings to resolve the matter, as she didn't want me to have a penny. However, at least that was after he died, and I was able to maintain a good relationship before.
Needless to say, my DH and I have tightly drawn wills to prevent this happening to our DC. I think most spouses just leave property to each other, trusting them to do 'the right thing' by their DC. DH can do what he wants with his share, but I would be livid if I thought all of my hard earned money might go to a stranger instead of my children.