No, it is unlikely they will weigh or take them through the sizer, but you can't totally rely on that. If the flight is full and you are near the gate then there is a small chance you may be asked to put the larger bag into the hold (almost certainly without fee) if the flight is full. But that is an exception. TAP's cabin size dimensions are about the same as USA airlines, so in metric TAP is 55 x 40 x 20 (44 litres), AA is 56 x 36 x 23 (46.3 litres) United is 56 x 35 x 22 cm (43.1 litres).