My advice - buy some good extension cords, plug what ever you want to run into them. Then stay close to the generator so you can unplug some of the cords. You are likely to do so when the refrigerators cycle to defrost or both sump pumps run at the same time. 3kw isn't much and that rating is probably optimistic anyway.

(We sure are getting a lot of "I want to do such-and-such with a tiny generator and almost no money" questions.)

Thanks for your quick response. Basically you've described the way we have been running for the past few years. So far, we haven't had problems with the load, but I'd like to make an improvement in safety and ease of use for the tennants.

My question is really about that neutral wire connection. I would like to understand why I can or cannot wire it as I've described. It should fulfill all my other requirements once installed and will be able to support a larger generator in the future.

I really don't know, but my first reaction is, "Not just no, but Heck no!"

You state these are two different services, two different meters. Hence they could be provided from two different transformers, fed from two different phases. Which would make the neutrals pretty far apart voltage wise.

I'll defer to the "experts" here - but why not buy two of these transfer panels and connect both to the same gen' set?

"Which would make the neutrals pretty far apart voltage wise."
The POCO and the previous electricians will have these bonded together. The POCO does so at multiple points.

I've never seen a transfer panel that coiuld handle two feeders.