Early arrival in Australia, early hotel check in not available

Most hotels will store your luggage for the day free of charge, so that part of the problem is easy - at least if you're staying in a hotel rather than an AirBnB.

As far as the ability to "freshen up", there are a few options.

The first is that there are public showers available at Sydney Airport. These are "bring-your-own-everything" style (ie, towels, soap, etc), and whilst they are cleaner than you might expect for a public shower, they are not exactly what I could call luxurious (and yes, I am speaking from experience of having used them) - however after a 14+ hour flight you probably won't care!

Alternatively some hotels will have shared shower facilities, often in their in-house gymnasium, that they will allow you use free of charge if your room is not available. The Westin and Hilton hotels is the Sydney CBD both have this option available, as I'm sure to many other higher-end hotels.

Other gymnasium in the city may also often the option of paying to use their shower facilities, although with 5 people this could get expensive quickly.

The final option is to pay for an early check-in at your hotel, or pay a day rate at another hotel in the area. Not all hotels will offer this, in which case you may need to pay for the night before in order to secure early access to your room.

Since you've gone AirBnB, this is a bit of a problem.

Hotel

Generally, the hotel's issue is that the room is not ready for you.

Talk to the hotel and ask them what your options are. Certainly they will cheerfully store your luggage, and may even put it in your room for you once your room is ready, so you can simply arrive back and collect your keycard.

As for freshening up, they may also have solutions for you there. If the hotel has a fitness center, it's an easy fix. Or they may have a relationship with a nearby gym, they may be able to get you discounted or free access.

It certainly won't be the first time they've encountered the issue.

AirBnB, cheap motel or other BYOservices

I don't see any probability of getting "freshening up" services in the same place as "luggage storage", outside of renting a hotel room, which kinda defeats the purpose of airBnB. So you'll need to do a fair bit of "running around" to get these separately, which will really bite into your day. Which means location will matter. And AirBnB's are often out in residential areas where services are different.

First, can you rent a car, at least for the first day? Put the luggage in the boot; done.

Second, look at Private Mail Box / Shipping Assist companies such as Mail Boxes Etc. They shouldn't mind storing your luggage, and they have lots of locations in residential areas where your AirBnB might be.

As far as "freshening up", I travel Amtrak a lot, and my style is "spongebath in the washroom" - and mind you, I am typically sweaty from having hiked all over Chicago during the layover. So I would just do that in any suitable public bathroom, in a little-trafficked area where the whole bathroom can be locked. Note that I bring all the "kit" to do this, including razors, washcloths and ziploc bags for the now-wet washcloths.

However if you want something a little more upscale, find a gym/fitness center - any of them will have a single-day rate for carte-blanche access to the facilities, including locker rooms. You can even swim or work out while you're there. Bring a lock. The gym will NOT have room to store your luggage, so you still need to solve that other problem.

I can see where this might not appeal. If you need the pampering of a proper hotel bathroom, then they have hotel day-only rates, which will let you solve both problems at once, though, at the highest cost.

Honestly, if you didn't have a car, the headaches of all that running around would "take the gild off the lily" for AirBnB as far as I'm concerned, at least for the first night. That's the problem - AirBnB doesn't have all the amenities of a hotel and experience at what travelers need, because hotels have been supporting travelers since they turned away Joseph and Mary.

I am not too familiar with Sydney (only been there twice for short visits), but here are some other options that haven't been mentioned yet.

1. buying lounge access in the airport. For five people, this probably isn't cheaper than a day-use hotel room, but will also provide food and beverages.
2. going to a swimming pool in the city. Not to use the swimming pool instead of a shower, that would be gross, but they do have showers, exactly like gyms.
3. I suppose showers are available, either free or at a small charge, for tourists in beaches such as Bondi.