Well, you are obviously well- intentioned! However, neutered or not, it is advisable to go with two members of the opposite sex. Also, dogs are primal creatures and your healthy dog may not appreciate the unhealthy dog's presence simply for that reason- just like younger dogs turn on the elders.
Even if you had greater harmony, the two dogs would fight to ascertain dominance, and then it would be settled.
Is playtime with other dogs necessary for your adult? Perhaps the premise is flawed- purely a question!