Short version: In terms of percentage, how did you increase your nanny or grandmacare pay with LO2?

Long version:
Grandma & Grandpa babysit LO1 for 40hrs weekly in our home. They get all school breaks off. We pay them half of what an in-home daycare here would be - that is the arrangement that is comfortable for us and them. We pay monthly.

LO2 is coming in February hopefully . March-May their hours will decrease to 24 hours a week, but we will still pay the same monthly total, even thought I'll be on unpaid mat leave. I just can't fathom paying less. They will still be caring for just LO1.

I have no idea for June-July because of travel and DH & I being on summer break.

But, starting in August, they will be caring for LO1 & LO2 back to 40 hours a week. I am not sure about straight-up doubling their rate... that is kind of a big amount for us to handle. I was thinking 150% of what they get now, so that LO2 would be basically 50%..... but... again I don't know if I'm cheaping out.

We also are trying to think long term. The preschool that we are thinking about for 2019 is more than double what we're paying them right now..... so in Fall 2019, our total bill would be XXX, which would be almost triple our current amount AND it would be close to an entire paycheck of ours per month, after taxes + health care.

ETA: FWIW, Grandpa gets a pension and a paycheck for an independent job (work on computer, travel sometimes). Grandma gets Social Security.