This is a pretty shallow league with 10 teams and only 9F, 4D, 2U, 2G.
With only 20 goalies required, they're not going to hold a lot of value and should be relatively easy to get your hands on. You're not going to have anyone pay anything for Dubnyk or Quick. They can easily be dropped.
Agree with the rest that I'm not trading the 2nd overall unless it's a win. I Gaudreau counter was bad and it sounds like you're not going to get a solid offer.
I'm good with moving Seguin, but coming off a down year I'm not sure you'll get full value for him. Keep trying but it might be better to hold him and hope he bounces back a bit.