The further the distance the less force gravity will have. With astronomical scales we can´t be sure how far away Nolan was and thus how strong the pull was. All we can say for sure is that at the distance they were the black holes gravitational pull had a larger force than the thrusters of the Thraxan spaceship and that Nolan was able to easily outdo that.

All i´m hearing is viltrumites (and other beings capable of interstelar travel on their own) can subconciously create wormholes or fold space. /J

I might be wrong, but isn´t Cecils position a secret in and off itself? Maybe Angstrom just didn´t know about him, while the Maulers are pretty public figures as supervillains.

Alternatively, if he did know about Cecil, he surely doesn´t know about his personality and it is rather suspicious to ask for the help of two notorious supervillains. I know i wouldn´t believe Angstrom if he told me his plan and would instead suspect he´s doing it for selfish/take-over-the-world reasons and would make sure i have a way to take him out whenever i want before i´d help him. Also if Cecil declined measurements would be taken to ensure the Maulers were harder to free. Meaning Angstrom might have to hurt innocents and i think he´d be more opposed to that against non-supervillains (stranding the Maulers in an empty dimension could be considered justified).