Both look like normal morphs; to sex them you need photos with the tail raised like in these:
Determining the Sex of Your Bearded Dragon - Hades Dragons UK
If you know Shrek is a boy, you should really think about separating them, especially with there being a large size difference.
If Fiona is a boy as well, they will almost certainly end up fighting eventually, even if they appear good friends most of the time. Males can do a lot of damage in a fight, even if there's never been trouble before.
If Fiona is a girl they may not fight, but you are likely to get other problems, such as Shrek dominating her (it sounds like this may already be happening as he's so much larger), as well as hassling her to mate etc. Males can become sexually mature at a fairly young age - certainly a lot younger than a safe breeding age for a female. This can present a lot of problems, if Fiona ends up becoming pregnant before she is mature. As they are related they should not be allowed to breed in any case.