How do I bring my jackbox games on a trip Without bringing my home PC?

Maybe.

Here are your options as I see them:

Persuade your in-laws to let you install Steam on their computer.

Pros:

• Probably the most straightforward solution.
• Doesn't cost any money.

Cons:

• You have to convince your in-laws to go along with it.
• You have to log into Steam on someone else's computer, which is a minor security risk. Make sure you have enabled Steam Guard, don't reuse your Steam password on any other sites, and be sure to log out when you're done.
• You might have trouble hooking the computer to the TV, unless they're right next to each other.

Try to run it on your laptop.

Pros:

• Jackbox is not the most technically demanding series of games. Your laptop might handle it just fine, even if it's got a weak graphics chipset.
• Doesn't cost any money (assuming you already own a laptop).
• You can test it in advance to make sure it will play well, and pick a different solution if it doesn't.

Cons:

• Doesn't generalize to more demanding games.
• Requires you to bring your laptop, which might be inconvenient.
• If you have a really weak laptop, Jackbox might not run on it.

Use a cloud gaming service such as GeForce Now

Pros:

• Can be used to stream to any computer regardless of computing power.

Cons:

• Usually requires installing client software, which your in-laws might disapprove of (so use the laptop instead).
• Requires a strong internet connection with low latency. Usually performs better over a wired connection. For a game like Jackbox, this might not be such a big deal if you don't mind a little bit of lag.
• Costs money.
• You probably can't test your in-laws' internet in advance.

Purchase a gaming laptop or a Nintendo Switch

Pros:

• This gives you greater flexibility the next time you need to travel.
• The Switch has a lot of first-party exclusives, unlike other consoles. As a result, it is a good companion device for PC gamers (in my opinion).

Cons:

• Costs money.
• The Switch does in fact have at least some Jackbox games available on it, but you would need to buy them again.