Steve Rogers.
Steve had managed to make it into the army. But Colonel Phillips had wanted someone else for the program so Dr. Erskine compromised. A few weeks later at the training camp Steve's lungs had given out. Bucky didn't find out until almost a year later.
Steve never became Captain America or met Howard Stark.
He did however have a date with Peggy Carter.
Tony Stark.
Sometimes his father was distant. But Howard Stark did care for his son. Since he had never met Steve Rogers, Howard was not worried about finding him, which made him give his son much more care.
Tony grew up in a loving environment and was still a genius, he never made any AIs since he didn't need any more friends.
Tony died in the same car crash as his parents.
Ovarian took over the company after the deaths.
Next will be Clint and Natasha. If you think something different should have happened instead of what I wrote let me know and I'll write what you want to see.
A/D not the best thing I've wrote but I'm always trying to improve.