Definitely NOT two at once, and not litter mates.
How old are your kids? Some JRTs don't do well with cats, kids, or other dogs, especially of the same sex (the dogs, that is, not so much the kids!).
Very few JRT's do well with cats, actually. They are prey driven. They will, however, rid your yard of all squirrels, rats, opossums, cats, etc.
My JRT Lab Mix brought a dead opossum back to bed with her after her 3 AM potty break. Her bed is our bed too... if that helps clarify the situation... 4 AM bed stripping....yay! Dead wildlife, in your bed, at 4 AM. Think long and hard about signing up for that!
I got a device called a whistle (Whistle Activity Monitor - Stay connected to your dog
) to track LuLu's activity because she is what I call a "6 mile a day dog". She needs two good walks plus some fetch and obedience training and lure chasing to not be completely climbing the walls. Sometimes, she still climbs the walls. For example, here is one graph from my Whistle:
I love to hike, and hike local trails weekly. So LuLu was picked specifically because I wanted an active dog to hike and camp with me, and help me work off a few extra pounds by requiring me to exercise her! My 17 year old son helps me out, too, when I just can't get enough walking time in with her. My husband runs her sometimes, and I have a thing that lets me attach her to my bike so I can get her a run in, too.
I worked from home full time for the first 2 months I had her, and I still work from home 2-3 days per week, so she spends very little time in a crate or alone.
Active is an understatement. If I still had school-age kids and worked in an office 5 days a week and preferred to watch TV rather than go for a hike this dog would have eaten herself a Terrier-sized hole in the wall and run for the hills. Thankfully I find her adorable even when she is a terror, and I don't mind being very active with her!
Here is a good example... last night we had to do something after work, so she only got a short evening walk plus some fetch and lure chasing in. Here is what she did between 6 and 7 AM: