Upgrading Axie tank, please advise on the best way to change?

Hi guys, sorry I haven't been about in a while. Been too busy talking to my Axies all the time lol! Anyway, They are in a 10 gallon tank at the moment which has suited them fine up until now because I had them since they were about an 1 inch long. But they are both at least 6 inches long now and getting bigger all of the time so I decided its time to change. I now have a 3ft tank which I think will suit the two of them fine when they become adults. I hope they will be happy in it. At the moment they are separated by a tank divider because Athena chewed off Aristotle's foot. They got on like a house on fire until 2 weeks ago but I think Athena is going through puberty as he's beginning to look like he's definitely a boy and I think he's trying to become dominant. I hope its only temporary as they used to be best of friends. At least in the new tank they will have lots more room.

Anyway, I have a plan in place as to how to switch tanks. What I was going to do is put them in my little hospital tank while we swap tanks over, then syphon the water from their tank out into buckets, move it out of the way and then put the new tank in place and put their water into it. Then I will add more water until I have enough in there. I will place all of the ornaments, some new and some from the original set up. I have a giant bamboo tube ornament for them to swim through and hide inside, another hide that has a bamboo like design, and more plants. As well as their bridge, rock and the cube with holes in that they love so much.

The question is, what do I do about the filter. At the moment they have an interpet pf1 filter but I don't know if it could handle the larger amount of water so do I change over to the filter that came with the tank which is a fluval 3 filter or use the one I have and see how it goes, or do I use the original filter along with another pf1 filter. I worry that the fluval 3 filter might be to much for them?

I just want them to make the change comfortably and I want to keep them happy. I also got a water pump with this tank but I decided to use it on my kids fish tank.

Definitely move the old filter over to the new tank. The old filter has the majority of the beneficial bacteria in your old tank. I would run the old filter in the new tank no matter what. If you want to switch filters, I would run both of the filters on the tank for at least a week before you turn off the old filter.
I use a marineland c220(about 40 more gph than the fluval), on my 3 foot tank, and I have no problems with flow.

ir you could put the filter media from the old filter into the new one