In most cases, the easiest way to replace hoses that go through inaccessible places is to link the new hose to the old and pull it through as you pull out the old. Use a male-male connector...cut the ends of both hoses as cleanly as possible...you want a smooth unbroken surface when you butt them together. Use PVC cement, 5200, superglue--anything that'll hol--to keep the hoses on the fitting...duct tape won't hold, hose clamps can get hung up.
Warming the hoses with a blow dryer or heat gun will make 'em easier to pull off their fittings.
From your photo it appears that you have just one tank under the v-verth for both toilets...which would make the run from the aft head about 4x longer than any marine toilet can move bowl contents without a lot of help from gravity...which means waste is always left sitting in the hose, and waste sitting in hoses can result in stinky hoses. So now would be the best time to add a second tank a lot closer to the aft head.
As for hoses...If you only want to do this job once, hoses are the last place you want to try to cut cost by going with the cheapest, 'cuz cheap sanitation hose will permeate in as little as a month or two. Raritan SaniFlex
RaritanSaniFlex hose would be my choice...it's been on the market for about 10 years now without a single reported odor permeation failure, and has the added advantage of being so flexible it can be bent like a hairpin without kinking.
If you'd like to discuss all this in more detail than is practical in a forum, you're welcome to send me a PM...I'll be glad to help you. If you have my book (see link in my signature), you'll find a lot of good information about how to replace toilets, tanks and plumbing in it.
--Peggie
"If you can't explain it to a six year old, you don't completely understand it yourself." --Albert Einstein