Read data from Quicken Essentials for Mac
Broadly speaking, I would create a virtual machine running Mac OS El Capitan and then install Quicken Essentials for Mac onto that. Once that works fine, I'd copy across the five binary files and test to see that they can be opened and viewed just fine from within Quicken Essentials for Mac.
Assuming this works as expected, what you need to do from here depends on what the end goal is, and the actual version of Quicken Essentials for Mac.
For example, if all they want to do is be able to view the data if/when needed, then exporting to CSV files may be all they need to do. These can then be imported/viewed in a plethora of software (including Apple's Numbers and MS Excel).
On the other hand, if they want to make full use of the data in a newer version of Quicken, then importing CSV files may not even be supported (depending on the version and platform, etc). In this case they may need to export the data into a different format (once again, depending on the version they have) and then using a newer version of Quicken (but not a recent version) or another third party app to import the data and export it into a suitable format for use/importing by the current version of Quicken.
The whole process is going to be somewhat messy as the absence of a common cross-platform file format was one of the biggest issues of Quicken software (not just between Mac/Windows, but between OS 9 and OS X versions and between PowerPC and Intel and so on). Intuit just never really handled things very well and lots of users got burned because of it.
I'd be happy to update/expand this answer when it's clearer what the exact situation is and what your relative wants to achieve.
UPDATE
Quicken stores data in a proprietary QDF file format, but has always offered options for exporting data into other formats. Unfortunately, the options offered have differed over time and with different versions.
This means you need to find alternative software that can either import data from Quicken's native QDF format, or software that can import data from one of the other exported formats Quicken has supported from time to time.
In most cases, the best workflow for migrating from Quicken to another product is to export the data from Quicken into either the QIF or OFX format. QIF is a format supported by many financial packages, while the Open Financial Exchange (OFX) format is used by banks and supported by most (if not all) financial packages.
Quicken's support for OFX has been hit and miss, but most versions have supported exporting into the QIF format. So if your relative can get their version of Quicken Essentials for Mac to export data into one of these formats then that's a good start. Otherwise it's a case of determining what format they can export into and then working out the best way forward from there.
As for an alternative to Quicken, there's a lot out there. Free versus paid and cloud based versus desktop based.
Banktivity
Assuming they're still using a Mac and want to run Mac native software, then one option is to use Banktivity1. Banktivity also offers native iPad and iPhone apps.
Two potential cons for this (depending on your relative's situation) is that the current version requires macOS Catalina or higher, and that they've now moved to a subscription model. However, if you don't renew you can still access and use the app - I think it's only the online services you lose access to.
If that's a no go, then the previous version did run on macOS Sierra and wasn't based on a subscription, but I'm not sure if/where that's still available.
On a positive note, your relative can try it free for a month and see if it'll meet their needs. This should give them enough time to test it's ability to import data (as it fully supports importing data from QIF files). This may be enough for them to file their 2020 taxes.
MoneyWiz
Another option is MoneyWiz, a very popular version for Mac and iOS users. This also supports importing data from CSV, QIF, and OFX files. I have personally used this app (on both Mac and iOS), and am very happy with it - although I have to admit it did take me quite a while to get used to how it works.
Also, I've never used it to migrate from Quicken so can't advise as to how easy this is or isn't to do. I do note, though, that they do have a support page entitled Importing from Quicken Essentials for Mac to MoneyWiz which actually suggests importing data from CSV files rather than QIF files.
From memory, they only offer a one week trial period, so your relative won't get as much time to test it out. They've also moved to a subscription based service, but do (or at least did) offer a one-time license option too (but I have no idea of the cost and what you miss out on if you opt for that).
GnuCash
GnuCash is not a product I have actually used, but it is free and has versions for macOS, Windows and Linux. Maybe even more.
It also supports importing data from QIF and OFX files, so it may be an option for your relative.
NOTE: Since your relative has 30 years of financial records, and assuming they get their current version of Quicken to work in a virtual machine, they will probably find it easier to leave their historical data in Quicken and start with a fresh set of records in whatever package they decide to migrate to. At least, that's what I've found many users have had to do when changing financial packages after a long period of time.

1. I am not affiliated in any way with this product, nor have I personally used it. However, I do know of people who have used it and are very happy with it.