Assuming they are OEM licenses then yes they are tied to the machine (specifically the motherboard), so if you bought the machine you can install that licensed version of Windows on to the machine itself. (see here).
Whether you can choose to transfer an OEM license depends on whether it was pre-installed or bought stand alone:
4. Transfer. The provisions of this section do not apply if you acquired the software in Germany or in any of the countries listed on this site (aka.ms/transfer), in which case any transfer of the software to a third party, and the right to use it, must comply with applicable law.
a. Software preinstalled on device. If you acquired the software preinstalled on a device (and also if you upgraded from software preinstalled on a device), you may transfer the license to use the software directly to another user, only with the licensed device. The transfer must include the software and, if provided with the device, an authentic Windows label including the product key. Before any permitted transfer, the other party must agree that this agreement applies to the transfer and use of the software.
b. Stand-alone software. If you acquired the software as stand-alone software (and also if you upgraded from software you acquired as stand-alone software), you may transfer the software to another device that belongs to you. You may also transfer the software to a device owned by someone else if (i) you are the first licensed user of the software and (ii) the new user agrees to the terms of this agreement. You may use the backup copy we allow you to make or the media that the software came on to transfer the software. Every time you transfer the software to a new device, you must remove the software from the prior device. You may not transfer the software to share licenses between devices.
So, (for everywhere other than Germany) pre-installed copies can't be transferred - if this is what came with those machines then you're good to go, slap a new hard drive in there and you can install the same version it came with originally, or use the keys to get an upgrade to Win10 as desired (any upgraded-to-Win10 license remains an OEM license tied to that machine).
While that explains the case for your laptops, if it wasn't a preinstalled (which is only really likely in the event of a machine privately home-built by the original owner) then there's a possibility that they could have transferred the license to another machine.
As @user253751 says in a comment:
What if it's the motherboard of Theseus?
While people are unlikely to have a motherboard of Theseus (it's more common for the motherboard itself to be treated as a discrete component) people do change/upgrade components in PCs all the time. The actual license text doesn't make a distinction for this, saying:
we grant you the right to install and run one instance of the software on your device (the licensed device)
and defines a "Device" as:
In this agreement, “device” means a hardware system (whether physical or virtual) with an internal storage device capable of running the software. A hardware partition or blade is considered to be a device.
The earlier link appears suggest that the motherboard is the line in the sand where Microsoft no longer consider it to be the proverbial "original ship".