Hi Edward...I am venturing where often no man dares to trod... into the realm of erections!
I do not know your exact size, but from your pictures it is quite possible you are larger than I am on average at about 9 x 7.5, erect. Now interestingly, my cock also can be 8.75 X 7.25 and be completely rubbery and soft. When I get strong sexual motivation, my erect cock can be about 9.25 X 8. I suspect your cock is a lot like mine. Mine is just so big that it would just as soon be rubbery as be hard as a rock.
When I was younger, my cock easily became erect ,most of the time, but if I overused it , sometimes it would refuse to get rock hard and would remain huge, but rubbery.
As I became older and my blood supply system became less efficient the times when my cock preferred to be rubbery as opposed to being hard increased in frequency.
Now at 75, I have realized that my cock cannot be used one or twice daily
and still be expected to get rock hard erections all of the time. In fact, if I practice having sex just every other day, then my cock is much more robust and becomes thicker and harder!
I believe the mechanics and physics of extra large cocks require special considerations. You could try jelquing too to tone up your muscular aspects of your cock. But most of all, I think you must realize that many , many men with 9 inch cocks and larger have difficulties getting rigidly erect! You were given a giant cock, but you were not promised that it could perform like an average cock!
My suggestion is to find a way of getting off and stick with that. Perhaps you can learn to have intercourse satisfactorily and perhaps you can not.
If you can not, it will not be the end of the world, my friend!