"Radiators" are somewhat mis-named because they're cool enough that they're largely convectors rather than radiators. Conduction will be bad for your leather (so don't put them so close that they're likely to get pushed against the radiator). Radiation is also bad, so watch out for sunlight or radiative heating by gas or open fires. But radiated heat from a hot-water radiator won't be a problem. So long as the temperature isn't reaching a point where you'd be uncomfortable, then neither will your leather sofa.
You should stock up on suitable leather dressings before they arrive and be careful about using them when needed, especially for the first year or two. Follow maker's recommendations, because the best solvents can depend a little on the quality of the leather and how it's dyed or sealed. This is crucial on pale leather ! (or on unsealed finishes like suede etc.) Most dressings will darken most pale leathers.
If it's an old leather sofa, find yourself (or make) some "British Museum Leather Dressing". The recipe is all around the place, it's basically shredded beeswax dissolved in hexane (flammable!) with some lanolin added.