If they have an artesian spring, then bottle it and sell it for $1.00 a bottle.
To locate, get a long pipeline type probe (about 3/8" in diameter) and probe around for soft spots underground. Find the spring, and if it is a localized problem, then place a concrete or better yet put in a plastic barrier and backfill with Wyoming Bentonite which is an expanding clay used to line brine pits and pits at landfills. Not much can be done if the whole yard is saturated except keep the sump pump in good repair and have a battery backup with alarm. Get a ryder added to your home insurance for sump pump failure since most policies don't cover it with the ryder.
To cap it, you will need to find it, have a well driller drill into it, set pipe and cement it in as deep as possible and then seal off the the pipe with a plug and cement. Everything depends upon the type of ground and formations you are dealing with such as a porous sand or a hard limestone, shale, etc. It could be hard to get a permanent seal.
Since it is the starting and stopping that wears on pumps, maybe a bigger pit would be easier on a pump. Every 3 minutes is what we deal with on a heavy rain so I don't know if it warrants the expense to cap a well or dig out the backyard to replace it bentonite.
Check the slope and make sure all surface drainage goes away.
Where are you at and is this a permanent lifelong problem or is it just recent maybe from saturation from this years rainfall?