Refurbishing everyday bikes
Depends how they've been stored.  If they were inside a garage or otherwise dry, then that's a lot less work.  If they were outside or damp, everything will be that much closer to EOL.

Gear changes and brakes: if there's been moisture in the cables then they can suffer but housings and inner wires can be replaced.

Tyres and tubes can degrade in heat.  Oils and greases will thicken and congeal so an all-round service of bearings can be in order.

Finally, why were they unused for a long time?  Was there a fault that was too hard to fix at the time?   Look for function. 

On the other side, sometimes a good wash, and a lick of paint can make an old bike appear very much nicer too.