Can iPhone SE logic boards be swapped to access data?

Technically, yes. But if the liquid damage is to severe the motherboard may not work at all.

Well unfortunately it sounds like a logic board fault, so as the data is stored on the logic board swapping this will not help in this situation.

The only way another functional iPhone SE could help is if a part is stopping the board from powering up such as the battery. Which is possible but unlikely in this case,

Sounds like you will need to speak to a data recovery specialist (There may be shops near you that can do board level repair to retrieve data, but be careful as an unskilled person could cause irreversible damage to the logic board). Alternatively there are a couple of online specialists I know of that do liquid damaged data recovery with a great reputation. '''https://www.ipadrehab.com/index.cfm?Page... https://www.ipadrehab.com/index.cfm?Page...

Only issue is these services are $300