Formula One champions' sons Nelson Piquet junior and Nico Rosberg are to test for Williams again.
Piquet, the 18-year-old Brazilian whose father and namesake won three world titles, will test on 3 and 5 February at Barcelona's Circuit de Catalunya.
Rosberg, also 18, will drive on 21 and 23 January. His Finnish father Keke won the 1982 championship with Williams.
Marc Gene is Williams' main test driver but another may be recruited before the start of the new season on 7 March.
Williams, championship runners-up to Ferrari last year, must also find an eventual replacement for Colombian Juan Pablo Montoya, who is leaving to join McLaren
at the end of the year.
Piquet and Rosberg both tested for Williams last month.