Take the offer, but then offer to your (now) former employee that you can help/consult/be available in the evenings or weekends for particularly difficult problems. Offer to do it for free and if they do value you, they might be willing to pay you for it. Your junior developers will be grateful but not as grateful as the owners.
This has worked for me twice in the past. You don't burn bridges, and in fact strengthen relationships. You will probably find, as I did, that your period of working two jobs will last less than a month.