I'm not sure how the nursing affects their ability to be cared for by others for such a short period of time? If they nurse prior to your session and after...?
I presumed there was something specific about your mother and MIL that made you wary of leaving the newborn.

I nursed for the first two years plus and didn't see any adverse affects from leaving for short periods like that 2-3 hours in terms of the nursing or bonding.