1 jack you'd want a minimum of 55gallons as they grow older. for 2 jacks, 75gallons is ideal. As they get older and mature you will see signs of aggression. Even a 20gallon is small for them to grow out in at 3".. a 29 would work better but I understand that's likely not feasible.
Best idea you could do? keep an eye out for a steal of a deal on craigslist and find a 75gallon to place in your room. See if you can do a father-son project with your dad and build a stand to fir the 75gallon. if that doesn't work you can buy warehouse shelving. In doing this, in either case, include a bottom shelf and you can store your 20gallon there.
There's always space, if you're willing to make the room for it

Someone said it best when they said:
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What furniture can we afford to live without?
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When that's been answered you have tank space! =D