I'll go along the lines of BCrider.

You could get a touring bike or maybe a cyclocross bike. The cyclocross has shorter chainstays, so it might feel a bit more responsive, but also a bit harder on bumps and the like. On such a bike, you will be able to fit wider tires than on road bikes, so it will be more comfortable on bad pavement and even gravel.

As for drop bars, the key point is to get them relatively close to you and at seat level. In other words, get them so you are comfortable using them without feeling stretched out, leaning too much and without any vision of the sky; then they will be even more efficient and comfortable than straight bars.

Another important aspect: the touring or cyclocross bike – or the hybrid for that matter – will also allow you to install front and rear racks, and carry some gear around; something which is useful if you ride for errands, and also essential for multi-day rides and tours. I think it would be a mistake to ride exclusively a lightweight high-performance road bike for 2-3 years, and then tour with a fully loaded bike: you would feel it slow and sluggish.

By the way, someone mentioned earlier on that "one climbs hills faster on a road bike". Well, that's not true (if you compare naked bikes). One striking difference, however, is that the typical road bike has tight gearing and fairly high low gears, which force you to stand up on the pedals, whereas a good touring bike has lower gears, so you may as well decide to stay seated and climb more calmly. The latter option takes more time, but is more restful, which is very useful at the end of a long day.

Finally, two other points.

1. You didn't say how tall you are. If you are on the short side (say under 5' 3"), a bike with 26" wheels may be a good option as it eliminates toe clip overlap. On the other hand, if you are sure you want to do a long tour with your son in law, it may be wiser to use similar wheel size on both bikes to limit the amount of spare parts you'll be carrying around. Obviously that doesn't work if you are 4' 10" and he is 6' 6"...

2. Does he live close to you? Are your riding styles (especially RPM) compatible? Riding a tandem might be an option.