It isn't relevant for you in div 5 to train IS for guards. You should train their passing though to atleast respectable. Then maybe some Js or so.
But he won't stay forever in div5, right? Not only because probably he wants to promote, but also because in two seasons' time, salaries of these two players will become unbearable for a div5 team. When you are making a "training plan" for a player, you also have to picture where will his owner be at the end of this plan. So if he trains that HoF until he is 25, I guess he will find himself at least in div3 at that time, look at his player with awful IS and think "why on earth didn't I train that".
So my answer is, I'd train IS at least to inept/mediocre, but mainly with 1 on 1 for Forwards and less with IS for C.