First... your two batteries are 62 amp hour each. That 675amp etc is a rating for engine starting. This number is fine for turning over an engine starter, but not for RV House Batteries.
Your batteries are Group 24. That's a basic size description. Because of a GP 24's physical size only so much storage can be built into them. 65 to 70 Amp Hours is common, but I've seen some more expensive models with up to 80 aHs.
The best way to determine if you need new batteries is to remove them, take them to an auto repair or parts store and have them load tested. But they're likely to tell you that one or both is shot. If one is shot then you must replace both.
Now, If you'd like more powerful house batteries able to provide more power to run things when you are not plugged into shore power or not running the generator you should NOT buy batteries like what you have.
Oh, you can buy Group 24 batteries if you wish, but I'd suggest since those batteries do not start any vehicle that you buy true deep cycle batteries that are made specifically for the duty you use them for.
True Deep Cycle batteries will cost more and if you don't ever camp without plugging into shore power then perhaps you won't want to spend the extra money.
By the way those batteries on your RV now are Wet Cell and require regular maintenance to stay healthy. If you spend extra for AGM batteries you'll never have to do any maintenance... ever, really.
Lastly, many people that do camp without shore power replace the two Group 24 batteries with Group 31 - a larger battery that typically has 100 aHs of power.
A good true Deep Cycle AGM Group 31 battery will cost about $280 to $350. So more than twice as much as the batteries you currently have in your RV. I'm not positive if Group 31 fit the Navion but I believe others here have switched to them without issue.
It depends on what you want to do, how you camp and how much you want to spend.
By the way, I'd be remiss if I didn't mention Lithium batteries as a choice. They are better by every measure, more power, faster recharge, zero maintenance and up to a 10-year life span, but they will cost about $1000 per battery. Cheaper in the long run probably. But not super affordable in the short term.
Hope all this helps. By the way House Batteries and battery types is a HUGE topic and one that can take significant study to fully get a handle on all the nuances.
Here's an example of a Group 24 AGM that fits your Navion and has 85 amp hours of true deep cycle power storage: