I should clarify a few points for JPLee if others want to chime in. What's being looked for is a Verizon CDMA smartphone, no LTE, on a Verizon MVNO. We are
not talking about generic 3G GSM. This means the hardware focus of what is being asked for is
Verizon CDMA only handsets that can be activated on Verizon MVNOs. There's not many options floating around anymore, especially of the more modern smartphone variety.
There's several hurdles that need to be addressed, and a few alternatives that need mentioned.
First... Verizon, as always, isn't that friendly to its MVNO wholesale partners and they do everything they can to make it hard on customers who use these providers. Keep this in mind moving forward.
Second, Page Plus/America Movil is using LTE to force customers into higher priced plans, but this actually isn't entirely Verizon's doing, it's more of an exploitative cash grab by Page Plus as the Verizon CDMA handset market dries up. That said, Verizon LTE network rates do run a tiny bit higher than CDMA network access for wholesalers; however, not all Verizon MVNOs who offer LTE activation restrict access to cheaper PAYGO and annual plans... just the crappy ones.
Third, given your FIL's habits, I'd stay away from phones without user replaceable batteries, minimum, and seriously consider going with ruggedized handsets as well. That means no Moto E/G/X, and no iPhone. You might want to also consider going back to a feature phone. I don't relish the idea of doing the parental-kid logic thing with parents, but perhaps if he can't take care of a nice phone, then he should only be allowed a reasonably rugged, cheap, feature phone.... especially if he's not the one buying these things. Also consider asking about what kind of handset he'd prefer (if you haven't already), if not ask if he actually wants to carry a phone at all. It's possible you're getting him handsets far more complex than he needs and something that he doesn't actually want.
Next, I'm inclined to ask how important Verizon coverage is for your in-laws. If AT&T coverage will work, I'm inclined to tell you to drop Verizon entirely and go over to either H2O Wireless or Truphone SIM. Cheaper phones with a far wider selection, and service as cheap as what you've been paying per minute and text (at least with H2O - Truphone could potentially be cheaper
or more expensive depending on usage patterns).
If dropping Verizon isn't an option, ditch Page Plus and go to Selectel instead
as they have 4G LTE annual plans that are technically a better deal than Page Plus (2000 minutes + 2000 SMS texts plus free roaming but no data, not 2000 minutes
or texts or 1000MB of data) for $100/year, plus there's the option of buying $10 flex cards that provides additional access at 5¢/minute/SMS/MMS/MB and is non-expiring for overages and data access on the annual plan. Switching to Selectel also opens up a whole slew of more recent 4G LTE handset options.
It's also worth noting that
Selectel's 3G CDMA only annual plan has the same 2000 minute + 2000 SMS text structure as the previously mentioned LTE plan, but only costs $75/year. The $10 flex cards can be used on this plan as well for overages and data access, and have the same 5¢ per minute/SMS/MMS/MB value.
Now back to the additional LTE handset options. Be forewarned shopping for Verizon LTE handsets.
Verizon's prepaid LTE handsets now require activation with Verizon Prepaid before the handset ESN/IMEI is cleared for activation on Verizon postpaid accounts and MVNOs. It's just better and easier to shop used with a clean ESN when it comes to Verizon handsets for use with an MVNO, CDMA or LTE. This is part of the reason why I encourage people not to stay on Verizon if they can help it.
As for actual handset recommendations... it just depends. There's at least six broader options you can go from this point, and they'll be shaped by whether you're willing to leave Page Plus or not and whether you can switch from Verizon to AT&T coverage. New or used carrier unlocked GSM 3G feature phone, new or used carrier unlocked GSM 3G and/or LTE smartphone, used Verizon CDMA feature phone with clean ESN, used Verizon CDMA smartphone with clean ESN, used Verizon LTE feature phone, or used Verizon LTE smartphone. I can provide you links to phone search tools, but I don't want to spend time researching handset options for six plus potential ways to handle this. I'd rather wait to see how you respond before focusing on hypothetical hardware recommendations.