Ok!! Thanks so much for the advice! We're filling it up, but a lot slower this time. It's almost halfway full again. The fish are doing great, but we're having bird issues now, the big rock hides(and cement blocks..they hide in the holes in them) are a little bit out of the water and so we had a ton of doves bathing in the pond. It just made me nervous, we had a falcon stalking the pond earlier(though all fish are accounted for!)
My parents are just not good at taking care of plants e_e most of them are half dead, but some are ok. They are all potted and can't grow too much, but I want to see if we can get some floating plants in there(so the fish feel more hidden and will swim through instead of just hiding in little caves)
I have a picture of right before the drama happened!

This is the first day we set up the plants

Here is a bit afterwords!
and one of my mom's photographs for her photography business(Just to show size comparison to a person)

These are all at an angle so you can't see how long it is...We'd have to stand far back, it's too long to take a normal picture of! I'm 5'6, and this pond is almost double me in length(somewhere between 9 and 10 feet, but really seems like 10) and probably 5 feet long on the other side. The pond itself goes a few inches lower than the ground, I'm not sure how deep it is, but it's pretty deep. About 100 years ago it used to be a feeding trough, but since then each new owner of the house has used it as just a decorative pond or a fish pond!
We pretty much have invisible koi though! Especially with all the drama, they just want to hide(and I don't blame them!)