First, I'm not a plumber, I just have done a shit ton of my own plumbing. That doesn't mean I know what I'm talking about.
If you are going to sell your house soon then a spigot on a spigot won't pass a home inspection. A spigot on a spigot is a fix but not a repair.
Soooo...
What exactly are you going to do under your house to your pipes to fix this?
If you're going to unscrew a pipe from a pipe fitting and if you see where you can, you should get some of these and screw them to the floor joist on the part of the pipe you aren't removing. That way you when you are wrenching on the pipe the other pipe that you're trying to free it from isn't twisting or bending.
http://data:image/jpeg;base64,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
I would still try to use a pipe wrench and twist the old spigot off the end of the pipe instead of crawling under the house and unscrewing the pipe the spigot is connected to from the part it's screwed into.