How practical might it be, to carry military tanks by helicopter(s) to remote areas?
Feasibility
The maximum payload of Mi-26 is:

20,000 kg Internal or external load.

The same page lists the following as possible payload for Mi-26:


2x BRDM-2 scout cars, or 2x BMDs, or
1x BMP or,
1x BTR-60/70/80 or,
1x MT-LB


All of the above are armoured vehicles and not classical tanks.
The 2S25 Sprut-SD is a self-propelled tank destroyer or light tank with a weight of 18 tons. So theoretically it could be carried by the Mi-26.
Other similar light tanks could also be carried. Or heavier tanks disassembled and carried (but as mentioned by Ralph J, that may not be very practical). The Mi-26 is routinely used to ferry heavy earth moving equipment to remote location.
With an C-17 or Il-76, main battle tanks can be (and are) easily carried and would be strategically preferable/more practical (see end of answer for more on same). Light tanks/armoured vehicles are also airdropped from the C-17/Il-76 (as mentioned by Ralph J).
Actual Practicality
However, locations where a tank could be practically employed (predominantly plains) would generally make transport by air and (then as required) by road possible. An example which comes to mind, is use of tanks by the Indian Army in Ladakh with induction by air using Il-76/C-17 and then further movement by road (of interest, that Leh airfield from where they are inducted is at 3,256m/10,682ft!, making it no easy feat).
In areas so remote that tanks need to be moved by helicopter, the use of the tanks (and note tanks are tactically best utilised only in more numbers and never in ones/twos) itself may not be feasibly/practical, so making the exercise futile/uneconomic.
Also, just getting the tanks would not be enough as you also need to move the large amount of fuel, ammunition and spares. These are no lesser of a payload in themselves.
So overall most probably not a very practical exercise.

C-17 ferrying Abrams Tank

Video on YouTube
Source: http://armedforcesweekly.com/c-17-globemaster-iii-loading-m1a1-abrams-tank/
Il-76 ferrying T-72 Tank

Source: https://defense-studies.blogspot.in/2016/07/main-battle-tanks-will-stengthen.html?m=1