I might suggest getting him tested for yeast overgrowth. If in fact he had overgrowth they will prescribe an anti fungal prescription(nystatin or something like that).
My son takes nystatin as well as a probiotic and with the probiotic we change brands every
so often .

Probiotics alone usually aren't enough to cause due off! If yeast is an issue, probiotics are a part of the treatment but certainly not a single treatment option. Natural and pharmaceutical anti-fungals may be needed as well as dietary interventions! Good luck- the yeast beast sucks! Lol

With most probiotics, you won't see much die off. Die off maybe with the meds such as Diflucan for yeast and vancomycin for clostridia. If you are using probiotics therapeutically, that's great. We are trying VSL3 next with Diflucan.

I wouldn't go higher - 2x a day is usually plenty. Are you expecting die off from yeast or clostridia and are you testing / monitoring these? We try to rotate with other probiotics.

I've done several courses of probiotics (various brands) with my DD and it's never seemed to make much of a difference one way or the other. Nystatin helped with her potty-training (she started going #2 consistently in the potty after resisting it for 6 months) but otherwise I didn't see any change in her behavior.