I have 4 ADSL UTP cables.
How much distance do I need to leave between cables to avoid crosstalk?
While it doesn't hurt to keep cables apart a bit you don't need to.
The ADSL links likely run for hundreds of meters in parallel outside the building anyway. It's essential to keep the pairs intact though. Don't split the single wires and keep the twist rate steady.
Alien crosstalk (AXT) really depends on a lot of things. The cabling materials matter most. Different cables have different tolerance agains crosstalk. Mostly it won't hurt the performance of those cables significantly by installing each cable a few inches away from each other.
Try to install them side by side first and see if the performance degrades. Moving them away 2 inches or more should probably eliminate significant amount of crosstalk if the performance degrades when the cables are placed directly side by side.