Explain to me in dummy terms the implications of these people agreeing to testify?

[Warpy]

16. Either they wanted to be the first to collect immunity

or if complete immunity wasn't offered, they want to go on record as having poor memories unless their noses are rubbed in actual evidence, in which case, they'll just sit there and plead the Fifth, over and over again.

Manafort especially won't be easy to budge on this, he's been a really bad guy for a really long time. Ditto Stone, who tutored under Lee Atwater. Not sure about Page or Flynn. I do know that some relatively minor player will eventually make a deal and sing like a little birdie at which point the big players will suddenly decide to retire to dachas near the Black Sea.