But it would seem pointless to introduce the 2 in the Anime if Ash won't get to battle them(Yea they could be there to be the people who run the gym when Dento joins ash) but it would be weird since they are trainers and won't even be battled? And it would be a good way to introduce the Monkey Trio too... all in the same episode/same arc.
Podda and Koon and their respective monkeys can still be showcased in a three-episode arc without Ash having to battle them. Boappa and Hiyappu can be used in battles against other trainers and Ash witnesses them or some other scenarios.
Either way, Dento's brothers/co-gym leaders will be featured before he decides to leave Sanyou to travel Isshu, much like Misty's sisters were seen when Misty left them in charge of Cerulean gym.