They want you to totally relax the anus which lets them push in further . Others want you to try to poo them out. You can try all three approaches to see which turns your guy on most. As a rule of thumb, circumcised guys like more pressure. The thicker the skin on the penis, the more pressure they like.
Simultaneous orgasm is quite easy to achieve.
The basic idea is just before the screwer is about to come, the screwee touches his own penis or the screwer touches it for him, using some lubricant. The combination of penis and prostate stimulation will take him over the top in a matter of seconds. Pleasure for the screwer mainly comes from contact between the penis and the anus. Pleasure for the screwee mainly comes from contact between the penis and the prostate gland, and from touching parts of the rectum quite far in. The prostate gland is on the front.