I have only had one Snakehead and one Poly in the past, but owned each of them (not together) for several years. Based on those two, and upon observations of fish owned by others, I'd have to say that this is just not a very good pairing. I'm not even gonna comment on that poor Angelfish...
Snakeheads are simply too aggressive in their feeding to expect them to allow a relatively slow eater like a Poly to get its share. Even with tongs, you'd be hard-pressed to get much food to the Poly until the Snakehead was thoroughly satisfied, i.e. way overfed. You might have some degree of success with tube-feeding, as long as the tube is opaque and thus does not allow the Snakehead to see the food inside, but even then it'll be tough. Same with a divider; your tank is pretty open and unobstructed, so you might be able to insert a divider at feeding time, as long as it doesn't prevent the Poly from feeding. Either method gets old pretty fast and soon stops being fun...ask how I know...
Fish need to be chosen with an eye towards compatibility; this means more than merely similar requirements regarding water chemistry, temperature, flow rate, etc. It also goes beyond simple aggression towards tankmates. Large differences in feeding response can and do result in problems such as less-aggressive feeders becoming stressed and malnourished, and/or more-aggressive feeders becoming obese.
I just saw this last post. If your Snakehead gets nervous when you open your tank lid, I must assume you haven't had it long.
If you think you are having problems now with getting food to your Poly...you ain't seen nothin' yet...
