4 5* Karels, what to do? Major help!!!!!!!!!!!!!

keep your +Spd and +Atk Karels. both have really good boons and banes. I would prefer the +Spd to secure more doubles, but its up to you. Unless you wanna merge them all together into a very strong unit, you can use your +def karels for fodder. Depending on your cain's IVs, he might be the best candidate to inherit a wo dao+ out of the rest of your 5*s. If you have a hana lying around consider giving one to her too

For now, save the Wo Dao+ until you get a hero that really requires it.
Other option is to merge them all together and get +3 Karel, which isn't necessarily a horrible idea. That +spd one with another 3 fed into him could be decent, but saving the weapon is better for now.

One of the Karels has a noteworthy IV distribution (+Spd/-HP). The rest I see are notable Wo Dao+ fodders. Honestly, Wo Dao+ is just too good to pass up as there are certain Sword units who lack in damage in general. Like Fir, Navarre, Lon'qu, etc....

Show us that Karel can be a good Uncle.

I have a +spd/-res Karel with a +1 merge and he's actually not bad. I had him benched for a long while because he's not that amazing but with L&D he's pretty decent (I only have L&D2 on mine). I used to have another one and gave Wo Dao+ to Palla but she got benched by Elincia so I'll probably feed her to a Hana.