Grayson Kristopher-----Fine, so long as you use Christopher.
Graham Miller---Like it, except that it may be said as "Gramiller."
Jaxton Miller---Hate it. Sounds like a hybrid of Jackson and......well, something else it should not have been joined with. The child will FOREVER have to explain to people that his name is NOT Jackson. Why doom him to a life of that?
If I combined options 1 and 2, I'd get Grayson Miller, which may be the best of them all.