Since Will was 4 years old 3 years ago, then he is 4+3 = <<4+3=7>>7 years old now
Dina is twice as old as he is so she is 2*7 = <<2*7=14>>14 years old now
In 5 years, Will will be 7+5 = <<7+5=12>>12 years old
In 5 years, Diane will be 14+5 = 19 years old
The sum of their ages at that time will be 12+19 = <<12+19=31>>31 years
#### 31