It is worth trying, I think starting with very young fish, i.e. 1" fish would give you a good chance of success. I also think your choice of a Loisellei as a tankmate is a sound one, they are they least aggressive Parachromis, but they are more than physically capable enough to defend themselves from the Texas cichlid. I would only be concerned if you choose another type of guapote, (like Freddies or Motaguense) as they would be more likely to impose themselves on the Texas cichlids, rather than simply defend themselves. Also, I would only go one with Loisellei, that way you would be sure to avoid the issue of the Loisellei paring off and spawning, things would not go well for the Texas cichlids if any equal sized breeding pair of loi's were in the tank.