My take is stop listening to venture capitalists. There is no right or wrong salary level. However, there should be a common understanding that there will be some level of sacrifice in the short-term, for the long-term. However, if your co-founders have real expenses, 150k or more might reflect that. A family of four, with student loans, living in a high cost area, when the person was making 250k...that sounds like a sacrifice to me.
On the other hand, if they want the startup to match the market rate job they are turning down to join the startup...that's a problem.
Or, if you don't have the money to pay, reasonable or not, you can't pay what you don't have.
An even bigger problem is if you can't have a discussion and work this out amongst yourselves - you have an even bigger problem. This is probably the easiest co-founder conflict you'll run into and you're not even officially co-founders. It only gets harder from here.