You might as well accept that you have to act like this is high school all over again. Hell, try forcing yourselves to stay quiet. You'd be surprised how fun that can be.
2. Switch it up.
The best way to have sex within earshot of your parents is to not have sex within earshot of your parents, you weirdos. Sneak out and try to have sex in your car, or the bushes, or your neighbor's attic. The adrenaline rush (especially in the last example) can definitely increase your libido.
3. Have sex on the floor.
This might be surprising, but your old twin bed is really loud and uncomfortable. Throw a few blankets and pillows on the ground. This way, you're not straining your childhood bedframe and sending awkward, constant squeaks throughout the house with each thrust.
4. Turn the TV on or something, anything.
This one should be the most obvious. No one wants their family members hearing them have sex, unless they're a crazy person. Hopefully you have a TV or radio or something you can crank up to hide the beautiful and awkward sounds of your lovemaking. PRO TIP: Don't crank it up so loud that it's obvious you're doing weird things in your childhood bed; you want it just slightly louder than normal volume.
5. BONUS TIP: You can still fly solo.
Just because you're by yourself this holiday, doesn't mean you're not allowed to rub one out. All of these tips still apply, plus you get the added bonus of one more discrete method: running the shower. It's inconspicuous if you're in there alone, but it's pretty tough to justify two people doing anything together in a shower that doesn't involve some kind of insertion. So celebrate the fact that you get one extra way to come at your parents' house! Nothing about that sentence is depressing at all!
Also, can someone show me how to block my parents from using the internet? I need to make sure they never see this.