From your description there are no easy ways to take care of your situation. Under the counter water filters would never be able to handle the demand from other sinks, perhaps two bathroom sinks at the most. Most, if not all under the counter water filters are for "potable" water. Your water source doesn't sound potable. Under the counter or small cartridge size filters (~12 in length) are only good for a few thousand gallons the most and none are designed to kill off bacteria.
The sulfur part maybe from the source itself and not contamination. South Florida, USA wells that are around 70-80 feet contained sulfur but from minerals in the ground. It stinks but it is used only for irrigation, not household use.
For microbe treatment, a chlorination system would be needed. This get expensive and many pieces. You need a pump to inject chlorine into a blending tank (~30-40 gallons). It must mix with the water for certain amount time to kill off pathogens. Next you'll need a large filter, more likely a sand filter, whole house size, then a charcoal filter to polish the water and filter out any other contaminants. It would not be potable but for washing, etc. it should be OK after you get the water tested. This is a must. It may become potable by adding a reverse osmosis filter, but again the water would need to be tested. Most RO filters for homes are for under the counter installation but the storage tank is generally no more than a gallon or two.
Then you have maintenance, the filter would need back washing once in a while and a constant source to purchase liquid chlorine. Also people living in the household would have to know how to check the chlorine storage tank so that the system is treating the water. To be safe the water would need to be periodically tested that it is safe.
