My father-in-law's bp is 70/100 and my pulse rate is 57? his age is 65. is it dangerous? what could be the consequences?

Impossible.: The systolic pressure (top number) can never be lower than the diastolic (lower number). If indeed you meant 100/70, that would be at the lower limit of normal. To determine if it's too low, check the BP sitting and standing. If it's 100/70 sitting and falls to a lower level upon standing, it's likely to be too low and might cause dizziness or fainting. He might be dehydrated.