I can see that you really are in over your head and I also believe you are making the right decision to give up Marley. Unfortunelty, making impulse purchases in pet shops is a very common thing and you were not immune.
Fortunely, you have come to the realization that keeping both Marley and Romeo plus your school, business and children are just too much for you at this time. The one things that does concern me is placing your ad on Kijiji. It is not a very good choice when it come to rehoming your puppy escpecailly since he is not nuetered. I am hoping that you will reconsider how you rehome him and chose a different form of advertisement or possibly surrendering him to a rescue. A rescue would be able to keep him in their care until he is old enough for nuetering. I would hate to think he could possibly end up in not reputable hands. Since you do not have any expereince rehoming a puppy this too can become an overwhelming task. If you would like send me a PM and I would be willing to help find a rescue in your area that would be willing to help you.