Wing05,
my case is similar to you, now my daughter is 15 months old, also take care by mother-in-law, but difference is she only take care of heib day time. My everyday's schedule is:
7.30 am
send HeiB from Tseung Kwan O to Central - mother-in-law's home (MTR & bus)
6.30 pm
bring her home
Sometimes dine in mother-in-law's home. I'll pump the breastmilk 2 times in the office. Evening, Sat & Sun direct bf heib.
So suggest you to try the same, cos same to Chingchingmom said, baby would like to stay with mother-in-law rather than with you if you only visit her 2 times/week.
Try it although it's not easier (becaues feel tired or incovenience), but you've to do it.