If the employees see the situation as open-ended and either long-term or indefinite, they are already shopping their resumes. There are only a few ways you'll keep them:
Have a definitive end
Show them definitively that there is an exit strategy for them to come back to the office, with a timeline that is reasonable/acceptable to them. Communicate that plan clearly to them, and stick to the plan, and engage them with the plan. If you are hiring new staff to work at that location, then include them in the interview process.
This plan can't slip and slip, or it will appear to be incompetent, or worse, theater to keep them indefinitely.
They travel on the clock
They don't get credit for their normal commute, nor are they asking for that. However, travel time, transit costs, mileage and tolls beyond the normal is funded by the company.
When I say "time" I mean their additional commute to the remote site comes out of their 8? Hour workday... So 2x45 min means their workday at the remote site is 6.5 hours. Or, if they're hourly, pay them an extra 2x45 min, but this does nothing to rectify the core complaint of having too little personal time remaining.
Do not fall prey to the logic that they are salaried so overtime is on them. That's meant for occasional application... in a customer emergency or code crunch, for instance... but making it business as usual requires an at least proportional salary bump (9.5/8 is +19%). If that number makes you gulp, then you understand the imposition you are placing on them.
If their wages are appropriately high, and the extra transit, fuel and toll expense is trivial by comparison, you don't have to sweat those. My lawyer doesn't charge me mileage.
Shortcut the transit
You said the new location is in an area poorly served by public transportation, implying the time loss isn't from sheer distance, and a private vehicle could get there much faster. You or the employer may need to provide the private vehicle. Then, this works in one of two ways. First, the vehicle lives at your home office, they commute normally to the home office, then pile into the vehicle for the drive to the work location. Or second, shortcut the transit:
If all your employees do (or could) travel to an intermediate point before coming to your main office, say they all come up the Sodor Line, ride through the Toppemhat station, to the Thomaston station near your office, a 20-40 minute train ride... Then a 10 minute wait for a bus... Then a 20 minute ride to the office. You store the van at Thomaston, and they all pile into it and ride to the remote office. Even better, if Toppemhat station is nearer the remote office, you do the same thing with the van at Toppemhat instead.
It's possible the vehicle commute could be quite reasonable, say 20 minutes from Toppemhat Station (a shorter train ride too), and their commute to the remote office could actually end up being shorter than their ordinary 1h commute. At this point it becomes an employee perk rather than a burden.
Congratulations, you now have a Scooby Gang with a Scooby Van, eager to take on other jobs too.
Sharpen YOUR resume
If the employer is going to be so unresponsive to these employees as to lose them, then you can't do good work there either. So make like the employees and quit. If you quit before them, you won't have to deal with their departures. Then poach those employees, they'll be easy pickings.
(Alternately the company considers your notice to be a wake-up call and says "wait, we did not realize the problem was that serious. Tell us what you need." And believe me it can be really hard for car-drivers to get what an imposition bad transit locations are.)
Of course, Murphy's Law says your new company will grab the contract for that same firm, so you'll be right back to "deja vu all over again"! Hopefully this time with a van.