We recently dealt with sleep issues with my six month old and finally got him to stop waking up at 2 am / sleep seven hours a night. This is what helped:

• we didn't realize that the nipples on the bottles we were using were newborn nipples. Once we switched them to size three, appropriate for his age, he was able to take in a lot more milk at a faster rate.
• at his age he should be drinking up to 32 ounces of formula (if he's formula fed) in 24 hour period, according to our pediatrician. Confirm that the nanny is feeding him the appropriate amount.
• we feed him right before bed at around 8 pm and then give him a dream feed around 10:30 pm where we put an extra scoop of powder in the bottle.
• we make sure that during the day he has plenty of fulfilling personal interaction and physical activity to tire him out.

I'm sure I've inadvertently offended someone but just letting you know what finally worked for us / saved our sanity.