Sheffield Wednesday have signed CSKA Sofia striker Sergiu Bus and Manchester United defender Marnick Vermijl for undisclosed fees and re-signed Watford midfielder Lewis McGugan on loan.
Bus and Vermijl have signed three-and-a-half-year deals, while McGugan will stay until the end of the season.
Filipe Joaquim Melo Silva has joined from Moreirenses for an undisclosed fee, subject to clearance.
The 25-year-old has signed a three-and-a-half-year contract at Hillsborough.
Bus, 22, has played six games for Romania's Under-21 team and scored 10 goals in 19 games this season.
The transfer of Bus, who has also had loan spells at four other Romanian sides, is also subject to international clearance.
Vermijl, 23, made one appearance for Manchester United this season.
The Belgium Under-21 international played the full 90 minutes of the Old Trafford side's 4-0 defeat by MK Dons in the League Cup.
McGugan, 26, made seven appearances during a loan at Hillsborough earlier in the season.
Meanwhile, Wednesday's Slovenian defender Dejan Kelhar has signed a deal to stay at Hillsborough until the end of the season.
The 30-year-old joined arrived on a short-term contract in August after leaving Red Star Belgrade in the summer.
He ruptured an anterior cruciate ligament soon after joining Wednesday and has yet to play for the club.
Kelhar has six international caps and has also played for Turkish side Samsunspor and Cercle Bruges in Belgium.