Think of a new puppy as a new baby. Can you manage two babies - the new pup and the two-year-old? That's the first question. Many animal shelters will not place puppies or kittens with families who have very small children. They encourage those families to adopt pets who are older (say, seven months old) because there's a better chance for them to do well. So you might want to give it some thought.
I think pets do grieve, but they also need YOU all the more. Let your elderly guy know he's still tops in your book. I'm told that sometimes an older dog really enjoys having a pup around - after the pup has learned who's the boss. If your older dog takes to the young one, it could be helpful. The New Kid will use the Old Kid as a role model, and you may be able to housetrain and teach obedience more easily. Personalities come into play in this. You want to try to see that they become friends. But you know that.
We have raised pups for Canine Companions for Independence, and we are required to crate train. I can't give you all the details on this post, but I can do the basics, and you can also get information from your pet store and/or your vet.
Crate training is the alternative to letting a dog run around in the house loose when you are away from home or at night. If you use the crate wisely (not as a punishment!), the dog will come to think of it as his own room and will like it. If he's left alone for hours in it, or put in there angrily, he's going to come to hate it.
You want to get a crate your dog can stand up and turn around comfortably in. We raise labs, goldens, or mixes of the two, so I bought an extra-large crate (the biggest one I could find, actually) and when we're getting a puppy I put boxes inside the crate to cut the inside space down to puppy size. It's too expensive to buy new crates as your dog grows, but you don't want him to have so much space in there that he can potty inside the crate and still have a comfortable place to sleep. The crate is in my bedroom, strange as it may sound, because pups feel more comfortable knowing that family is nearby.
When there's a new puppy, I put old towels in the bottom of the crate (comfortable to sleep on but easy to wash), and I give the puppy something safe to chew on. To make the crating more attractive, when I put the pup in it I also toss in a TINY little treat - maybe a little piece of a puppy biscuit - to help him decide that this is a good place. At night, after I've taken Puppy out to do his thing, I'll put him in the crate, close the door, and put a towel or something over the door to shut out light, views of people, and other distractions. Expect some fussing! If you can wait out the whining and barking (think: toddler crying, "I don't wanna!"), then he'll get the idea that this is what is supposed to happen. After that, you'll know that when he cries or whines in the crate he's doing it for a really good reason (i.e., has to potty, has a stomach upset).
I do just about the same thing during the day when I'm teaching him to stay in his crate. I crate him after he's answered the call of Nature outside. I start out by being out of the house only about twenty or thirty minutes. Then I come back, let him out, praise him, and take him outside right away. You can't leave a puppy in a crate very long, not only because he'll be insecure but also because he can't go without pottying very long.
When a toddler gets overexcited or overtired, he or she can get out of control. In the same way, a puppy who is overexcited or overtired sometimes makes into big trouble. Then a time-out may be in order. You treat this as a normal occurrence, without getting angry at the dog. Just put him in his crate with a chew toy and shut the door. Compare it with putting that out-of-control toddler down for a nap. When you let Pup out, don't do it angrily.
It takes lots of patience, but I think it pays. Your puppy has a comfortable, happy place of his own, and you know he (as well as your house) is safe.
This post is long enough, but I'll be glad to answer any more questions if you want to contact me.