First off, will Jenny get bad ideas if the other dog isn't as well trained as her? Say, it doesn't come when called, will Jenny stop coming when called?

Well, dogs dont actually learn by observation, so no, if one dog doesnt know come, your other dog wont learn not to come anymore. However, there are some things though that dogs do that are social or have to do with survival (such as eating, drinking water, potty, etc) that they often "copy" each other on. Have you ever seen one dog go to the water bowl then a bunch of others join in? Or one dog digging a hole and the others join in? But they cant learn any obedience type stuff from each other.

What changes? Like what is the difference, walking one dog compared to walking two?

Depending on your dog(s) it can be near impossible to walk 2+ at a time. Especially if one or both are active, or if one or both dont have perfect leash manners. I RARELY walk my 2 together, and its only when they both have their gentle leaders on. My 2 are very reactive, especially when they see another dog, and they feed off of each other- so instead of getting a little aroused, they get double as barky/worked up when together and a dog walks by.

Will it not be as attatched to me as Jenny is?

This all depends on the dog. Some dogs tend to attach to one person, some love everybody. And much of it also depends on how important/relevant you are to the dog. For example, who walks the dog, trains it, plays with it, feed it, etc. It has little to do with how loved you already are by another dog, etc. Sometimes dogs may be more attached to each other than to people too, but again it mostly depends on the individual dog.

Now, whenever we watch a movie, Jenny will quietly lie on her bed. If we got another dog, would they both lie down, or would they be up playing with each other?

Again, depends on the dog- their temperament, their age, breed, etc, and it also GREATLY depends on their mood. If they are both adult dogs and have had enough exercise that day, yeah I imagine they would both lie quietly. Dogs, like people, are all different and have different moods. My dogs are 3 & 4 yrs old, so they mostly just hang out and mellow around the house, but there are certain times of the day that they get excited and start racing around, wrestling with each other.

How do you keep the fastest eater from fighting for the others remaining food? Or would they not be able to both eat in the kitchen? (my mom isn't fond of the idea of them not eating in the kitchen, because it would ruin the carpet)

Many dogs learn to work out their relationships so they dont fight over resources. (Took my dogs only a week before they stopped arguing over everything, though of course there are some items that are higher value and they do occasionally scuffle, but for the most part theyve learned each other's boundaries). Ive also heard many people have taught their dogs to eat together and only out of their own bowls. But in general you cant really expect any dog not to eat unattended food. Id say the solution would be to feed them far enough apart that they arent tempted to eat each others food, and once they finish pick up any left overs until the next meal time. If your current dog is free fed, Id recommend switching to timed meals.

Would they fight over the 'best' seat in front of the fire?

Maybe always, maybe sometimes, maybe never. Like I said, most dogs figure their boundaries and relationship out in a short time. Some dogs dont guard locations, some do. Some dogs dont guard toys, some do. Some dogs dont guard food, most do. lol A lot depends on the dog. Most dogs I know usually share spots and beds and greatly enjoy each other's company.

How do you tell the difference between play, fighting for dominence, and 'real' fighting?

Its challenging. You really have to see a lot of it, and ideally have help from a professional or book to spot everything. A dog that has been properly socialized around other dogs between the age of 8 wks-18 wks will have learned to ritualize the pressure of its bite so that it will never do any damage when it bites. So even if it gets into a real fight, it wont do any damage. That said also, dogs rarely get into real fights that actually need to be broken up (I have never seen one in my 4+ yrs working with dogs professionally). They do however OFTEN scuffle. This is usually very loud, over the top, lots of teeth showing, pawing, etc. Again this is all very ritualized in a properly socialized dog and rarely leads to any damage. Dogs are social predators meaning they walk around with deadly weapons in their heads (teeth/jaws) yet they have to have a way to communicate with each other safely. So evolutionarily dogs have developed very complex ways of communicating and arguing without hurting each other. If they didnt, the species wouldnt have survived!

And a biggie, because I've heard a lot of different opinions on this one: Are two dogs not much more work (than one dog is) or a LOT more work (than one dog is) ?

Depends on the dog & your lifestyle. Its definitely a lot different than just having one. There are a lot of pros and cons. I found it very helpful to have a 2nd dog to play with and entertain my 1st dog. They often wear each other out. But at the same time, they have very different needs and behavioral challenges that make for twice the work in a lot of areas. In general I think a 2nd dog isnt too much different than 1, as long as they are a good match. 3 dogs though is very very different.