Do not lie or try to play any games, they are better at it that you are. Have you lawyer there, let him talk, you say nothing.
Well you can't turn back the clock. Think very carefully about what you said (the human memory is terrible), writ it down, give it to you lawyer, let him do the talking from now on.
And are you saying they are registered MGs? Just because someone put a serial number on something doesn't automatically make it a registered NFA item.
You're missing the point. The should be destroyed, inoperable, when you turn them in. When and how they got that way, let you lawyer talk.
Famous last words. Just saying this tells us you are in trouble, Call a lawyer!!
Knowing and proving are two different things. Before you, the last person to lay hands on them is in China... think about this.
Get a dam lawyer and STFU.