Five are realistically possible on the Peninsula: Weddell, crabeater, leopard, Antarctic fur and southern elephant. No single landing is likely to hold all of them, because each one follows different habitat.
Weddells are the regular sighting, around coastal fast ice and further south. Rounded face, spotted coat, and a habit of looking entirely unbothered. Crabeaters are pack-ice animals, so whether you see one depends on whether your route reaches accessible ice. Fur seals get more noticeable at South Shetland sites later in summer. Elephant seals turn up at selected sites but are far more a South Georgia animal.
There is a sixth, the Ross seal, and it is exceptionally rare on a standard itinerary. Plenty of experienced guides go a whole career without seeing one.
The crabeater seal does not eat crabs. It feeds primarily on krill, and its teeth interlock to strain them out of seawater. It is one of the most numerous seals in the Southern Ocean, which still does not mean you will see one.
A word on the seals that look asleep. A hauled-out seal might be resting, digesting, warming up, moulting, nursing or hiding from something. Long stretches of stillness are completely normal, and it is not a sign the animal is ill or unaware of you. It may be highly aware of you long before you see it move.