Handstands and basic calithetics are always possible, but I think you need to get outside and cut your teeth on some real brick and concrete if you want to seriously improve. That said, handstands are great for developing good prioperception, which is crucial in Parkour. Start out just leaning aginst the wall. You'll probobly have to kick up with far more strength than you think the first few times. Just hold it for as long as you can. Make sure to shrug your shoulders "up", tense your core and legs, and try to keep everything nice and straight. Oh, and keep your hands shoulder-width aparta and spread out your fingers.
Once you're compfortable with that, try finding some space in the family room (or what-have-you) and start doing free-standing handstands. You may want to practice how to bail out of a handstand first. You'll either simply "walk" down by moving one foot, and then the other slowly down underneath of you, or you'll have to roll out of it. I reccomend walking down, as its slower and safer, and with practice, you can "pirouette" and walk down at any angle.
That's about the only thing I can think of that would really count as training for parkour indoors that also wouldn't mess up the house! Good luck!
