Sorry you had two of your villagers die like that.

Good advice was given here. I always let me scientists relax when I click on them and see that's what they're doing. As far as I know there's no way we can make them go for a swim, relax, etc.
As others have said, keep an eye on their health bars and if they dip down, take them to the food bin. You may have to do this multiple times. Sometimes you'll get a message that says, "Your villager feels better after eating."
I also take mine to the well and have them drink. It may take a few tries as they may want to water the crops or the field instead. You can also try having them swim in the waters of the lagoon.
Giving them a break and putting them on farming or healing is also an excellent suggestion people gave you. I've had researchers live to be quite old, but those ones had breaks in their "career" as farmers. :] My oldest villagers tend to be farmers, doctors and even builders.
Did you get any indication they were going to die other than the health bar being down? Did they become sick first?