Yes, please don't laugh as I hope we didn't mess up terribly and we're still working on getting the bikes...working.
May I ask what you paid just so I can understand your investment in these two bikes you bought, 2 identical, right? You can PM me privately if you want to share some info that way too. (Look for the PM button to the right of this post where my info is.)
1) First off, I think you got a decent 1st basic eBike that could be modded, if needed, to work for your needs. To keep costs low see if the seller will fix the problems. Can you describe specifically what the problems are too?
2) It looks like the stem for handlebars can also swivel to swing back towards the rear to get the handlebars closer to you. Otherwise, you can get some sweep back bars that would look cool on that bike & give you a "no reach" feel for good control leverage & turning, etc.
3) You can get a spring seat for bumps & put one of those gel "blubber" pads on it too for vibrations, if needed, so you could lower the seat if you can't with the seat tube you have now. You have a frame with no top tube, so getting that handlebar adjusted or replaced with your seat lowered should get your feet well planted on the ground.
4) Once you get this bike repaired & ungraded, then you can determine if it's good enough to pull the dog & trailer. I highly recommend you go to Craig's List & search on bicycle trailer to get a feel for what's in your area. You might search on electric bikes just to see what pops-up too. Also, check out Portland OR & other big "bicycle cities" to get an idea of the types of trailers that are available. Also, check out Amazon for dog/bicycle trailers.
5) To keep costs low & still do what you need, if you can't return the eBikes for refund or decide not to, then you can upgrade your existing setup without getting into complicated upgrades. Believe me, you do NOT want to play around with this as a challenging DIY project, imo, unless your husband is really, really, into wanting to spend hours, days, weeks figuring this all out for The Love of eBikes. We're eBike "freaks" in here, and so we are fantasizing, eating, sleeping, drinking eBikes for some strange reason. It's not normal.
6) If you need more power or better brakes with the dog trailer, then we'll have some ideas for you. To K.I.S.S. (keep it simple silly/stupid) I would only upgrade the DD motor setup you have now. Better wait on that to see what we can do with what you have now. This upgrade may cost between $300-$600 per bike, but no sense in worrying about that now. There are too many options.
7) I'll stop here on a lucky number. You're very brave to attempt this. Ride very slowly without the trailer & with the trailer sans dog to get a hang of it. Preferably in a parking lot, wide empty bike path or empty level street for practice. Then add the dog & repeat. Then try the hills you will actually climb with/without trailer/dog.
Hey, we're going to want to see some videos once you reach your goals with this eBike. Lots of good people here, so I'm sure someone is going to get you fixed-up here one way or another! If you end-up ditching these eBikes, then you might get a good used one from someone in here in the Wanted or For Sale Sections on ES. Or, maybe Craig's list might have some in your area often enough, so you could test ride it in person. We could give you feedback on any "finds" you locate too.
Best of luck to you. You have amazing challenges ahead, but you know "the saying" that when you can come-out the other side you can/will be a changed person in unexpected & positive ways too. So, somehow looking back, there can be some beautiful sunny days without the clouds of doom worrying you anymore. Acceptance & loving each moment & all the little pleasures we have each day; that's simply what's in the remaining journey of what we all really have. Looking forward to the joys you will find in your simple day to day eBike travels too. Something lost now found again and cherished so much more!
Btw, what dog will be hitching your rides?