At the party staged by 3 young couples the following leaflet was distributed among the guests:

"Who now are 3, will soon be 6
And gladly we confess it.
But how we've chosen you may know
As soon as you have guessed it.

Tom, who is older than Jim, is Dorothy's brother ,
Virginia is the oldest girl,
The total age of each couple-to-be is the same,
No two of us are of the same age,
Jim and Lisa together are as old as Bill and Dorothy together."

Who got engaged to whom?

Abridged from: 101 PUZZLES BY C.R.WYLIE Jr (1957)