Do I get new tires and how many?

I have a 2006 Honda Civic with three tires I feel need to be replaced, but one that is still good on tread. The readings are 3/32, 3/32, 4/32, and 7/32. The less worn tire is newer, and by the manufacture date, appears to have been put on the vehicle right before I purchased the car used in 2013. The three lowest ones all have a leak that costs ~10 psi a week so I'm constantly having to fill them, and they are the worst tire I have ever used, thus I want to replace them. Is it recommended to replace all four tires to match, or just the three bad ones?

Also, if I were to consider selling the vehicle soon, should I even bother to replace the tires? Will it affect how much I can get for the vehicle if it has fresh tires rather than old tires? I don't exactly want to spend $500 on new tires if the vehicle can be sold for the same with or without new tires.

If you were keeping the car, I would suggest getting 4 all new tires. Even though the 7/32 tire still has ok tread remaining, it's now between 4 to 5 years old. Tire rubber hardens as it ages and hard rubber just doesn't offer the same traction that newer, more pliable rubber does.

But if you're selling it, get 3 of the same make and model of the one still ok tire.

You may not get all of your money back from a new set of tires but it makes selling the car much easier. It is also a negotiation tool for you to keep potential buyers from low-balling you.

You need 4 new tyres

With a front wheel drive car (honda civic) get a pair of good quality tyres for the front cos these take most of the braking,+ all the acceleration+ all the steering, so your life depends more in these that the rear 2
(its important these are new and the same manufacturer+kind - cos tyres from different manufacturers, even different kinds from the same one, can have different driving/braking characteristics. If different it could cause you to spin if braking hard)

The rear can be a cheaper kind (but should still be the same)

If you are selling in the near future I would buy 4 new ones the same (cheap ones) - they you can advertise it with 4 new tyres (always a good selling point) I would all keep the receipt for them just in case the buyer doubts they are new - but don't need to show the receipt showing they were cheap unless you need to

Just get 4 new and matching tires and be done with it. You don't want mismatched tires (especially of drastically different ages) on your car if you can at all afford it.

If it makes you feel better, mount the existing tire with 7/32" of tread left on it onto a cheap steel wheel or a junkyard-sourced wheel and use it as a full-sized spare if you really feel like you're wasting that tire. It's always nice to have a full-size spare anyway if you're doing much long-distance driving or don't want to immediately deal with replacing a flat/damaged tire - donut sized temporary spare tires can't really be driven even 100 miles safely so a full-sized spare could get you wherever you're going and back without an issue until you have time to get the replacement tire you want, at the price you want to pay and/or without having to resort to having the car towed somewhere etc.

Replace all 4 of them at the same time, you will get more for it if you do.

A new tire sales company will only replace tires in pairs, so get 4 tires. Keep the best one as either a spare, or sell it on Craigslist for $35 if you already have a decent spare.

You never get extra money for the vehicle because you have new tires on it. I'd recommend taking a cell phone picture of the car and put it on the "Letgo" site. You'll sell it right away. You may want to check out the average value of the vehicle in your area before deciding what to sell it for. Look up your cars value on the Kelly Blue Book website.

Tires should always be replaced in either pairs or the entire set of four. The two 3/32 tires need to go immediately, and the 4/32 tire is not far behind. I would be best to replace all four. Or if you plan on selling the Honda very soon at least replace the two 3/32 tread depth tires.

I would just replace 2. No use wasting money and polluting the environment by replacing perfectly good tires. I would put two new tires on the drive axle to prevent excessive wear on the differential.

"If I were to consider…" Means you're not, at least for a while.
In this case, I would replace all 4. If I were to be driving it, that is.
It's a problem for you now, so fix it.
If you were to try and sell it with those bad tires, anyone who cares enough to look will offer less.
As in: if I must buy new tires right after I buy the car - I'm not paying your asking price.
Get a rep for selling junk and it will stay with you - another thing to avoid.

What does the spare look like?