With 8 month old twins, I can sympathise with the incessant crying problem. I've found this British baby resource v. useful - www.babycentre.co.uk

In particular, for when it gets really bad, there's a helpline called "Crysis" - if you can afford to call a UK number, call +44 207 404 5011 and you'll speak to someone who can help you cope

On the question of "leave to cry or not" a great book called "Why love matters" strongly advocates NOT leaving babies to cry it out - it can raise stress levels in the baby's body, and cause permanent, long term problems due to prolonged, elevated cortisol levels. Even if it doesn't stop the crying, cuddling lets your distressed child know you're there, and trying to soothe him.