Are you making them on-site employees or remote employees? If they are on-site, you buy licenses for them. If they are remote, they are contractors and they buy their own licenses.
That dispute of people walking away with licenses is because you share the serial number with them. You should buy for yourself and your own office.
If someone else works remotely, they should buy it themselves as you have no control over their time. They could be lying to you constantly delaying your project while collecting money doing nothing. Have you thought about that?
Our company have our own licenses for multiple employees - UnityPro, AndroidPro, iOSPro, Team. For example, if we consult for you, we do not ask for fees to buy UnityPro or Adobe or AutoDesk licenses.
If you buy UnityPro for them, what’s next? 3DMax for others, New computer for others, Android tablets for others, Car loan for others, Home loan for others, Free vacation to the Caribbean while supposedly working for you… you get the idea where this slippery slope is going. They then insult you and walk away with all your licenses and equipment.
You might want to consider asking them for their resume and portfolio, or collection of arts done. Are they using their real names? Does the PayPal show a different name or alias? Are they sufficiently skilled enough to complete your project?
Have you considered doing background checks to ensure they do not have criminal records and their Degree certificate is not fake? Does the background check show multiple addresses - indicating they are on the run and hiding from creditors?
You might want to give them a simple art test to make sure they do not do stick drawings, modelling test where they model low-poly and good quality works, coding test so the coder knows what they are doing.
If the cost is too much for you, you might want to consider full-development companies - IronBelly, Rosor, FlamingHairBall who can do all the work for you and they seem to have good reputation. You give them the project and they do all the work for you.