The office of the Grand Ayatullah Khamenei:

The required distance between two Friday prayers is one legal farsakh‌ and the criterion isn't a straight line between the two points, rather, it is the conventional route people take to come and go between the two points. [In the case of there being two conventional routes], if one of the routes is shorter and one is longer, according to obligatory precaution, the shorter one is to be counted.

The office of the Grand Ayatullah Sistani:

In the mentioned case, the second Friday prayer is void, unless the first is lacking in some conditions of validity.

The office of the Grand Ayatullah Makarem Shirazi:

The distance between two Friday prayers shouldn’t be less than one farsakh, and in the case of two Friday prayers being offered in less than that distance, the first will be valid and the second void and the criterion is the route used by most people.

The office of the Grand Ayatullah Safi Golpaygani:

In my humble opinion, during the occultation of the twelfth imam, the Friday prayer doesn’t replace the Dhuhr prayer and it is necessary that one who has offered the Friday prayer to also pray Dhuhr prayer, nevertheless, offering Friday prayers is permissible, and if the distance between two places using the conventional route is over one farsakh, holding Friday prayers in both is permissible.