If this game comes up for ranking I will be opposed to any monsters without a damn good argument for why we should rank one even though they apparently share names with better-known monsters in more played Dragon Quest games (oh hi needless votesplit), and there's a precedent for not ranking such things from Lufia 2 and FFT, etc.
The big difference between monsters in DQ5 and something like FFT is that you absolutely have to use monsters for at least the middle third of the game to even fill out your party member slots as you only have 1-2 humans max; most probably will use some for a good while longer, especially with the larger party in the remake. In this sense they're more akin to FFT generic humans, except with fixed skillsets. Of course FFT generics aren't ranked either, but then FFT has a huge glut of bosses ranked, something that would never happen with DQ5, not even in an alternate universe where it had FF7 level popularity in the west. There's also nothing I'd consider a good representitive generic class from FFT, whereas DQ5 has an obvious one.
If DQ5 had the popularity it did in Japan, I'd say that ranking a couple of monsters (Slime Knight, at least) as representitives of the game's only really distinctive gameplay system would be a no-brainer. Considering that it'll be around the minimum threshold of acceptability at best, though, they're probably not worth bothering with.
Yes: Main character (Does he have a canon name?)
Reliable posters on Gamefaqs (Aeana and Hopeful Death/n00b averager) posted that Abel was listed in some jp guidebook or another. Then again, they also gave default names for the son and daughter different from what the English version used, but it's better than nothing I guess.
That aside, my personal thoughts on what to rank-
Definate yes: Hero, Bianca, Parry, Madchen
Bianca is very clearly supposed to be the intended wife, they even plaster art of the kids with blond(e) hair all over the official site. She's an obvious pick to me, and if we only rank one wife it's obviously going to be her. Other three need no comments.
Leaning yes: Sanchez/Sancho
He plays a fairly significant part in the plot, I can't imagine anyone forgetting who he is. There's a risk that a lot of people won't use him as a PC, but checking a guide/stat topic for one PC like this shouldn't be a big deal. There are plenty of ranked games where the average player won't (or can't) use every PC and will have to stat topic/abstain on them.
Maybe: Saber/Borongo, Nera/Flora, Henry
Saber's someone that I'm guessing most people will use, for gen 2 if nothing else, but it's pretty bland in the DL. No real personality either. Wouldn't strongly to ranking it, but I don't really see much to gain from doing so either.
Nera is basically Bianca with better stats and a really crappy healing move. The near-clone status makes it easier for people who didn't pick her to vote on her, but it also means that ranking her alongside Bianca doesn't really add much. Open to arguments either way on her.
Henry... he's a temp who leaves pretty early on, but he was by far the best developed character in the original version, so he's pretty memorable.
Leaning no: Deborah, Slime Knight
Being DS-only is something I could live with, being three-way pathsplit alongside that... yikes. It'd take a strong argument for me to support ranking her, especially since she's clearly not the canon choice. Slime Knight (we could rank him as Pierre, or whatever the first SK defaults to in the English release) is the only monster I'd consider, but given the low drawing I'm inclined to say no.
Definate no: Tuppance, the fairy whose name I forget, Pankraz/Papas, any monster besides SK
Abstain: Bosses. All of them were completely unmemorable in the original, but it sounds like they added some actual beef in the plot here so I'll let remake players decide on this.