THe cable car doesn't go to SEA aquarium nor particularly near to it. Its not really designed for being a transport method in the way you plan. For the idea above you have to get to Mount Faber, use the cable car to Mount Imbiah and then walk a mildly complex route through the building site. Then at the end of the day you have to either discard half the cable car ride or go back to Mount Imbiah and then get off Mount Imbiah which is normally a cab and unless its around a popular meal time they arent that common up there (or you use Grab). It would be far better (IMO) to treat the cable car as a ride from Sentosa and back to get the full ride and see things in both directions of travel. You could then walk to SEA. The route is complicated by the building works where the Merlion used to be but its broadly this: Come out of the Mount Imbiah station through the shop, pass the Skyhelix tower and walk towards the old colonial building in front of you down a broad avenue - thats the Madame Tussauds/Images of SIngapore building. As you get near follow the railings round to the left and you will spot a staircase down (and if they have fixed it an escalator). Go down these to the Sentosa cable car lines Merlion station. If the building is still ongoing you will have to follow signs as they move you around based on what works are ongoing. Cross the main building site to get to the Imbiah station of the Sentosa Express Monorail. Again follow signs round the building screens to get onto the Sentosa walk that will take you either to the BullRing in front of Universal where you then bear left or go through the Resorts World area/Festival Walk from the bottom of the last staircase on the Sentosa Walk to get to the same area - for both you can do this by following signs to SEA which is on the waterfront.

To get out at the end after the gift shop? Yes there is. It is marked on the Park Map which you can find on the attraction website under the Plan your Visit tab.

Child tickets are chargeable from the age of 4 to 12. So if you enter with the two children, you will need an adult ticket for yourself, a child ticket for the 6yr old and the 2yr old is free.