Haven't driven a car since the start of the pandemic; can it be driven without special measures?

Cars are routinely left parked for three to six months or more without running, with no ill effects. I wouldn't hesitate to jump it and see if it'll start. As @BrianKnoblauch comments below, jumping a completely flat battery risks the alternator. The risk can be ameliorated by using a battery charger first, or leaving the jump battery and the to-be-jumped battery connected for a time, so the flat battery has at least some charge before the starter is engaged.

If the battery was old when the car was parked, however, the just-sitting may have pushed it over the edge into failure. That is, you might be able to jump it into running now, but the battery won't start the motor on its own the next time.

The low-tolerance-for-risk solution is to replace the battery. If you or your in-laws want to gamble on getting stuck, make sure the battery is fully charged, either with a charger, or by driving the car a significant distance. Without figuring alternator capacity, I'll guess that "significant distance" means an hour at engine rpm well above idle.

If you have the ability and access to some tools, remove the battery and bring it to your local national auto parts chain ie: AutoZone, AdvanceAuto Parts, Oreillys etc. You may want to call first to see how they are handling this during Covid. They will charge and test the battery to determine its condition generally for free. This will take several hours or possibly overnight. Reinstall the battery. You may want to cycle the ignition key from "off" to "on" several times before attempting to start the vehicle. Start the vehicle as normal. Let it idle for a minute or two until the engine idles smoothly. Drive slowly (25-35mph) around the block for a few miles to warm everything up and get the fluids circulating. Gently apply the brakes several times to remove any surface rust from the rotors. If everything seems ok find the owners manual and check the maintenance records. If it is due for service based on time or mileage then schedule that service. It may be due for an oil change because it has been a year since the last one.

One thing I would do is check all the fluid levels before starting it, even if only to drive it to get it serviced. Also the tyres may need some air. My brake discs rust easily in our wet climate, so I know after even a few weeks to be wary of them at first. A few uses from very slow will tell you if they're OK and getting back to normal.

As I commented, I'd ideally charge the battery from a dedicated charger before starting the car with it. If it fails that test you definitely need a new one. If it passes, you still need to be careful when the weather gets cold as batteries don't like being kept discharged. Luckily failing to start is most likely when the engine is cold at home, reducing the chances of a stranding.

One other thing to check: regardless of the amount of gas in the tank:

Actuate the gas gap release lever NOW. You want to be sure the cap will open, while there is enough gas in the tank to get to a mechanic in case it doesn't.

My 2010 RAV4's release lever seized, after only 6 weeks of non-use at the start of the pandemic.

Battery

First thing you do is throw the battery on a battery charger. These are simple machines with a red and black alligator clip, and a common electrical cord. They supply 12V-ish power, and have a voltage regulator so they will correctly charge the battery without overcharging.

A typical battery charger worth owning is 5-12 amps in normal mode. (may also have a ~2A slow charge mode and a 20-60A boost mode, but you want normal mode).

More amps never hurts, but it costs money, and you don't really need more. Slam-charging a battery with lots of amps will prematurely age a battery.

A typical battery is 80 amp-hours new, so you can do the math on that, it may take 8-15 hours to fully top up the battery.

Allowing a battery to go stone dead is also bad for the battery and will age it somewhat. Car batteries are very, very bad at deep cycling (being run down dead then fully recharged).

Unfortunately, lots of things reduce their life. Using them, not using them, overcharging, letting them go flat, looking at them cross-eyed... generally if a car battery is older than 5 years, it's on borrowed time. So if an old battery has gone dead, you can try to save it with a slow (~10A) charge, but be prepared to say goodbye.

Is that a terrible battery design? Oh you betcha, but it's cheap, and it's good at one thing: the huge surge of energy needed to start an engine. You can get a 40-year battery that weighs 500 pounds (nickel-iron) or 500 dollars (nickel-cadmium e.g. airplanes), and lithium batteries show some promise but they're expensive too.

Fuel and consumables

For a storage period of months, you really don't have much of a worry. The worst problem you will have if your area has winters, is "winter fuel" vs "summer fuel", which has different boiling points; just put fresh fuel in there when able.

Even out to a year, this won't be a worry.

Once you're out past two years, you have to start worrying about the fuel turning into varnish in the tank and equipment. Ask anybody who started up a lawnmower that's sat for 10 years, you can spend an hour chipping varnish out of the carburetor bowl. And those are super simple carbs.

These days, everything is fuel injection. Varnish will break the fuel pump, plug filters, plug lines somewhat, and mostly, plug fuel injectors which are extremely fine because they make a fine mist of fuel. Fuel injectors can be sent out and cleaned.

Another issue is the 10% ethanol in the fuel breaking down and turning into stuff that is corrosive, which can then rust the tank interior and in particular, the delicate brass electrical connections for the fuel pump and fuel gauge sending unit.

Watch for coolant problems

The other issue with extended storage is coolant. It doesn't evaporate, but rubber hoses can rot or be chewed by animals who are making their home under the car since it never moves. This can cause a leak, either immediately or later when the system pressurizes. As such, once you get the car going again, it's easy to accidentally run the car with no coolant in it. The car won't tell you anything until it overheats, by which point damage is starting to be done. Unfortunately most people do not take overheat warnings seriously, and continue driving "because what else can I do?" This will warp the cylinder head, greatly increasing repair costs... and eventually reduce the engine to slag.

What you do is pull the car over as soon as practicable, let it cool down for 1/2 hour, then try adding water if you have any... and if you are able to refill it and the leak is slow enough, try limping it to a nearby place it can be serviced, again shutting off and letting it cool if the overheat light returns. Sometimes that works, sometimes it doesn't. If that is not viable, then just have it towed. It's cheaper than resurfacing a head.