Fallout – How to get the dwellers back in the shelter after exploring

There is no way to force them to use them, they will just use them on their own until their stock you give them when you send them out goes away.

Nothing (that is in the game right now) can cause them to die in a single attack that they would not be able to heal from so no worries there. When they get up to the radiation amount a RadAway would heal then they will use one, then their health is low enough for a Stimpack to fill it up, they will use it.

A good ratio is 2 to 1 from Stimpacks to Radaway. I generally will send out my guys with 20 Stim Packs and 10 Rad Aways though they will often still return with a RadAway or two on them. I will also do 15 and 10 if I am low. Your residents will never need RadAway unless you run low on water so as long as that is ok do not fear sending more with your guys in the wastes.

There are three factors.

Luck, luck, and luck.

Luck determines how many caps wasteland explorers get, and how many caps you get for successfully rushing a room's production. I believe, however, that the caps you get from leveling up a dweller is not affected -- they provide caps equal to their new level. Reach level 4? That's 4 caps. Obviously if you have 200 level 48 dwellers, you'll be raking in the dough soon enough.