How do I exactly calculate the amount of heat generated in MOSFET?
Power generated in the MOSFET will be

P = I x I x Rds

10A x 10A x 0.055 ohm (max) = 5.5W for one, so 2.75W for two in parallel.

The 0.055ohm is with 28A, could be less with only 5A.

You can find MOSFETs with even lower Rds, such as AOD508, with

Rds of 3 mOhm @ 20A, 10V

10*10*.003 = 300mW generated power to dissipate.

https://www.digikey.com/products/en?keywords=aod508