Hi Gary
Yes, I use GEDCOM files from my genealogy software. You then still have to go through all possible merges, but it imports names, dates, locations, possibly even sources if the software has them properly (I mainly attach the image as source in my software, so that doesn't help for WikiTree and I have to add a proper source to each profile) and it also imports connections / relationships. For me it's a huge relief, because WikiTree doesn't accept my European way of dates, so I would have to add them manually. Gedcom somehow exports the dates that WikiTree accepts them.
Important thing for Gedcoms is to use small files, I recommend something around 200 profiles. I usually go to the "oldest" ancestor and then export all descendants. Of course this always exports the same few relatives of me, but when you have good work in both software and WikiTree, then merging doesn't take long. Might depend a bit on your surnames - very common names will give you more possible matches to look through.
Gedcoms from Ancestry might take a bit more time to clean, as Ancestry often exports what we call "junk" - lots of information that isn't needed for WikiTree, often double information on sources.
As your parents already did a lot of research, I think an offline software might be helpful for you. There are many different softwares, maybe you want to try some until you have one that fits with your needs. They usually have a proper way of dealing with sources and usually they have a name index with years, which helps a lot to work with hundreds of relatives.
Then I suggest to get to all the photographs as soon as possible and write down who is who, when and where was the photograph taken etc.
And then later you can add all information and maybe photographs to WikiTree :-).