You might want to look at buying a dog play pen for when they go outside to potty.
This is the type that I am talking about -
http://www.amazon.com/Pet-Trex-Premi...217781-3550230
- this is just panels that connect together to make a small fenced in yard.
At 24" tall, you will never have to have anything higher with them being so little.
They will quickly learn that when they are outside in 'their' yard, they are supposed to potty.
When they are older, you can have them out with you in the yard, when they know to come and other commands. Then you will have better control of them. With the fenced in playpen, you won't have to worry so much about the wildlife in the area. We lived on the outskirts of the Great Dismal Swamp, and when we had our French Bulldog, we had to worry about bobcats, bear, hawks and eagles. Even full grown and 17lbs., there was still the dangers to deal with.
You should probably get them a small crate to be their 'den'. Dogs deal with things better when they have a safe place to go to when things (noise, activity, etc.) gets too be too much and they retreat to their bed. If you get a place carrier with the door on it, leave the door open during the day and then tell them to go to bed at night and close the door.
Rest assured, if you start working on a routine with them, they will quickly learn. When I foster pups, they are supervised and go out at least every 2 hours, if not more. You may want to start with newspapers on a tile floor for accidents. But the sooner you set a routine, the better.
Good luck. And know that for every ounce of love, and second of time you invest in them, will be returned 10 fold. Just love them, which I know they will.