I put Mosi onto adult food at around 9/10 months so I'd say Jess is ready to go onto adult.
I'd get some hills adult to mix with the kitten and gradually transition him over to the adult. There shouldn't be much difference in the ingredients between adult and kitten of the same brand so it probably won't upset his tum, but still a good idea to change over gradually.
re the wet - because of the high water content it's usually easier to change over to something different without digestive upsets so I'd just feed the kitten pouches and when they're finished give him some felix adult pouches.