Teaching 2 cats outdoor cats become indoor kitties

I'm moving to an apartment and I need to teach 2 cats to become indoor.
They've been outdoor cats all their life, they can stay inside our home or outside as much as they want.

One of them is 8 years old, the other one is 4. Its going to be tough for them to learn they can't leave the house anymore.

The 8 year old cat is very smart (for a cat), would that make it easier for her to get used to living in an apartment? the good thing about her being older is that she's becoming more sedentary.
the other one acts like a kitten. He likes to play around alot, I'm not sure how well he'll get used to living in a place where he can't run around or climb trees anymore.

Living in an apartment is a choice beyond my control. My parents have decided to move there.

I have so much questions! I want to make it as easy as possible for them because just by moving to a different place is going to be tough on my kitties
.
* how can I make the move easier for them?
* what would be the best way to make them used to being indoor cats?
* am I going to have problems with their weight? they won't be as active and I'm worried obesity might become an issue.
* how long do you think would it take for them to get used to their new situation (I know every cat is different but having a general idea might be useful)
* what are the pros and cons of an indoor cat? having indoor cats isn't common in my country, I don't know anyone who has an indoor cat to ask them.
* how can I know if they are depressed? I'm worried they might become miserable. I know they won't be as active as before so I'll have to rule out noticing how active they are.
* is it difficult to train a cat for walks? (like dog owners take their pets for a walk)
* is there a big chance they might jump from a window? I'm so scared that might happen.

any info at all is helpful at this point. I feel so sad to have to change their whole living situation.

thanks for reading.

*I made a mistake in the title.. sorry about that.

Ohhhh I'm so excited! Don't feel bad, your cats will be perfectly happy once adjusted and healthier and safer! Really it is best for cats to be inside.

As for your questions, I'll do my best and then offer some links!
* how can I make the move easier for them?
Make the move easiest for them by putting them in one room while packing everything up with all their stuff and just their stuff, move into the new place, and then bring them with you on another separate, just-cats trip. Have everything settled into the new place, and then bring them into the new ready-made home and put them again in one room with all their stuff for just a little while. There are tons of threads on different ways to do this with lots of advice!
* what would be the best way to make them used to being indoor cats?
My advice? Let your cats outside still for the remainder of when you're in the house you live in now, and once you move, never let them out again. This way they have to adjust to everything all at once and not going outside becomes a part of living in the apartment. Others I'm sure will disagree, it's like a preference for ripping off a bandaid quickly or slowly.
* am I going to have problems with their weight? they won't be as active and I'm worried obesity might become an issue.
Actually, now that you have total control over what they eat, its less likely for them to become obese. And they don't need to be less active. Get them scratching posts, toys galore, interactive toys to play with you with, etc.
* how long do you think would it take for them to get used to their new situation (I know every cat is different but having a general idea might be useful) Not long at all. When they meow at the door ignore them completely, distract them with a toy, or leave the room. Do not punish them.
* what are the pros and cons of an indoor cat? having indoor cats isn't common in my country, I don't know anyone who has an indoor cat to ask them.
Indoor cats are less exposed to cat diseases, less likely to be attacked by a human, car, or other cat, or other animals, do not get lost, you will catch health problems more quickly.
* how can I know if they are depressed? I'm worried they might become miserable. I know they won't be as active as before so I'll have to rule out noticing how active they are.
They will not be miserable. Buy windowsill perches for them to peek out at the outside world, more toys and such for them. They may get stressed out since so much is changing at once, but when they settle in it will be fine.
* is it difficult to train a cat for walks? (like dog owners take their pets for a walk)
It is not difficult. I live in an apartment and take Zissou out on a leash all the time. It is very important that you use a harness and not a collar. I would also wait for them to get used to both the changes in everyone's lives and being indoor-only before you try this, and some cats will not do it period, esp at that age.
* is there a big chance they might jump from a window? I'm so scared that might happen.
All your windows MUST have screens that are locked in place. Also, it is very important that you train the cats not to lean on them-- easy to do, especially if you buy them windowsill perches. When my sister first got screens she put double sided tape on them so the cat would stick slightly if it leaned on them.

Good luck, here are some more links with advice:
http://www.hsus.org/press_and_public...e_indoors.html
http://www.hsus.org/pets/pet_care/ou...rs_or_out.html
http://www.hsus.org/pets/pet_care/ca...y_indoors.html
http://www.nssvet.org/ici/index.php
http://www.caws.org/indoorcat.html
http://www.scvas.org/index.php?page=text&id=keepcats (scroll down for more tips on the transition!)
http://www.towncats.org/articles/article1.html
http://www.pawsperouspets.com/tips/catindoors.shtml

And we're all always here for the other questions that come up along the way!

There isn't really anything that I can say that Zissou'sMom hasn't already said just to add that cats are really adaptable and I am sure that they will cope just fine

just wanted to thank Zissou'sMom for all the links and answer to my questions. It was very helpful!

Randdom thanks for the encouragement, I really hope the get used to their new living situation soon.