From memory re ambulance rides, there aren't really any other seats where children could sit.

If you really don't have anyone to ask to come & sit with your kids, you need to start asking for support. I'm assuming your hubby will be away for work purposes - if his employer needs him that urgently then perhaps they should step up and provide some additional support. Work asking about. Alternatively if you've ever used family day care or a babysitter, those are the people you could approach. People are very happy to help, you just have to summon up the courage to ask for help.