Thank you for your advice. I will bear in mind there is not double standard when dealing with them both. As best I can, I try not to give more attention to one or the other. My Chow tends to be the jealous type as well.
 
My Chow Chow listens well and hopefully the young lady will learn by example too.

SUMMARY
Generally, the 2nd adult dog (referred to as "he" although female dogs are included) needs more time than a 2-month-old puppy who adopts the same elimination area of the incumbent. The new 2nd adult dog's mind is not a blank slate and he has his own mindset.  He may not want to adopt the same toilet area as the incumbent as he is also territorial. So he urine-marks or simply wants a clean elimination area unless he has no choice. Confinement in a room or by tethering is still the basic principle of toilet-training in young or older dogs. The main problem is that the time-pressed Singapore owner usually has no time to conduct the training when the new adult dog arrives. So he or she eliminates all over the residence, making re-training very difficult.  Dog do get jealous and seek attention too. Therefore, owners need to be aware of this.    Consistency, perseverance, authoritative commands (firm tone of voice and eye contact from lady owners and caregivers) and positive reinforcement (food treats and praises) and patience are more important in such cases. If the command is like that of a friend, it may not have any training impact and the dog may ignore the trainer.