If a girl was cheating on her spouse and both males came in her. Will this increase chance of pregnancy. She was came in inside of the same week. Stopped seeing her mistress, got her period, then go pregnant. Could the child be both of the males child ?

If there is any doubt, a DNA test needs to be done to be sure.

No. It is impossible for two sperm to fertilize the same egg.

If she is pregnant with twins both men could be the fathers.

If she had a regular period between the two encounters, baby would be from the encounter after her period. If there is any question as to whether the bleeding was an actual period, then DNA testing would need to be done, as some women will have bleeding at the time of ovulation thinking it is just an off period.

If any doubt, for any reason, a DNA test should be done.

Either man, could be the father, so, a DNA test will need to be done