Flying from Sweden to the UK via Amsterdam on a single ticket (i.e same airline) everything happens inside the airport.
Since your parents are elderly, perhaps they could sign up for 'special assistance' and let the airport staff guide them through. I've used special assistance numerous times at different airports. I don't know if Schiphol has translators available but special assistance staff are usually pretty good with people who have communication difficulties. They usually offer a wheelchair or buggy and you just let them take you through.
