i would recommend you to choose grand livina since u mentioned the primary use is for family leisure.
sentra and livina doesn't share the same engine code.
but both share quite the same tech, timing chain, coil on plug and if im not mistaken livina is electrically driven power steering which the sentra dont have.
i dont have experience driving grand livina, just a passenger based experience only.
but i do have experience on sentra. this car is heavy, with the standard QG16DE engine, the power to weight ratio is not good. it is quite comfortable though. rear seats are big enough to occupy 3 persons medium size body. parts are quite source-able from half cuts.
many of my friends who owned sentra 1.6 have experienced engine overheat. why? as i stated before, the power to weight ratio is not good. to pull a 1200+ kg body with an oem rated on crank HP of 98hp is really bad.. (bare in mind, case was in an AT sentra)
grand livina's gearbox are suited differently as it is an MPV. ratios are different from sentra, hence u can expect a good power delivery through out driving.
but its up to u... whatever car u choose..my tip is:
1. drive the car. make an assessment.
2. sit beside the driver and let the car dealer drive the car. make an assessment
3. sit at the rear seat of the car (for grand livina, try 2nd row and then the last row) let the dealer drive the car. make an assessment
both 3 steps above are quite good to distinguish the car satisfies u or not. hope this helps, thanks