Northern Ireland international defender Hodson, 21, has been a member of the Hornets' first team for three years, while Italian Under-19 international striker Trotta has previously been on the books of Manchester City and Napoli and scored eight goals in eight games during a loan spell at Wycombe last season.
Both players are available for Brentford's clash at home to promotion-chasing Sheffield United in League One on Saturday.
Mark Warburton, Brentford FC Sporting Director, told the club's official website: "Marcello is a player we have admired for a long period.
"He had a very successful loan period at Wycombe Wanderers and has been very near to joining several Championship clubs over the last few weeks. We are delighted to welcome him to Griffin Park and look forward to what we hope will be a very beneficial loan spell for all parties.
"Lee has made almost 100 appearances for Watford in the Championship and has established himself as a regular full International with Northern Ireland."