For reference I live in a valley but within five minutes of town, in the county over daughter lives on the lake on a hill. Son-in-law usually travels up north of here and southwest, never out of contiguous. We own our property, no HOA so antenna shouldn't be an issue, price is tertiary to quality and reliability. Currently nobody in family is licensed, though I think I'll get GMRS soon for camping and might as well get ham done too
To get any meaningful coverage you are going need a repeater. To reach your son anywhere in the contiguous US without relying on anyone else's infrastructure, you will absolutely need HF radio.
HF radio: that pretty much means amateur radio, unless you are a business.
It also means that everyone will need to get their own amateur radio license.
It also means very large antennas, especially on vehicles. Like, huge whips and a lot of hardware. Handheld HF radios are not really a reliable solution, and still require large antennas.
It also requires a lot of knowledge on behalf of the users. It's not like you select a channel and just use that, to deal with ever changing atmospheric conditions, you would constantly need to utilize different bands/frequencies, as well as deal with a lot of other users.
Not trying to discourage you from HF radio, but it is an expensive undertaking, requires very large antennas, a lot of user knowledge, and a certain amount of luck. It does not guarantee communications at any time.
VHF/UHF amateur radio bands can give you some decent coverage if you get on linked repeaters, but again, it requires a lot of user knowledge and won't guarantee communications. Those linked repeaters still rely on the internet, plus random volunteers purchasing and maintaining their equipment. Each user will need their amateur radio license. Good antennas are required, as well as user knowledge and frequent practice with equipment.
Plus, zero privacy and all the repeaters/frequencies are shared.
GMRS is an option. One license covers your whole family. Range is pretty short on its own. A well placed repeater can extend range, and there are sometimes existing and open repeaters that you can use. However, repeaters are not always open to public use. Repeaters cannot be legally linked, so range is limited. Still going to require base radios, mobile radios with external antennas, etc. Frequencies are shared, so no privacy and you must share with everyone else.
Leased service can do what you want, but you'll be paying monthly for system access, radios are leased from the provider, and it still relies on the internet to link sites. This can get pricy. No license required, as that's covered by the company leasing you the equipment.
Satellite phones/devices are probably the most reliable options, but you'll pay a lot. Satellite phones will get you the coverage you want pretty reliably without lots of user knowledge like amateur radio. Devices are expensive and so is the service. But it'll do what you want. Any event that takes down the satellite is going to be big enough to impact everything else, so worries of relying on satellites is kind of pointless. There are two way messaging devices, like the Garmin InReach units, and they work very well. It's text based messaging only. Devices are a few hundred bucks, and you are looking at anywhere from $7 on up for monthly service per device.
There are also two way radio like satellite devices from companies like Icom that will give you what you want, but the radios are expensive and so is the service. They also don't perform well under thick tree cover.
I've been in this industry for 30 years now. I've been a ham longer than that, and held a GMRS license for decades. I fully understand your goal, but you are going to have to make some compromises. You either need big radios and bigger antennas, as well as a lot of user experience, or you'll be relying on the internet to get the coverage you want.
As for putting up your own repeaters:
Repeaters are not "plug-n-play" devices. They are very complex and require a lot of knowledge to set up. The test equipment required to set one up properly can easily run you in the tens of thousands of dollars, plus a lot of required knowledge to work the test equipment. Repeaters require a lot of maintenance and installing one will either require a tall tower, or paying someone to put the repeater at their site.
If I was trying to do what you want to do, here would be the plan:
New cellular phone that has satellite capability. Most newer ones can do this, and the major carriers can support it. It's not 100% perfect, but it's the cheap and easy solution that doesn't require amateur radio licenses and lots of user knowledge. If you want Push To Talk type service, you can get apps that will do that quite well.
There are also walkie talkie like devices that work over the cellular network. The device looks like a regular hand held radio, but utilize the cell network to give you coverage anywhere the device can connect to the network. Some services will allow connection to several carriers, so it'll pick which ever one is available. Still, no coverage where there is no cell service.
There really isn't one perfect solution, and anyone that tells you there is doesn't understand how any of this stuff works. You have to pick which ever one suits your needs and fits your budget, and then deal with the individual shortcomings. There's no way around that.
