What to do when you "skinny fat"

Hey,

So, I am trying to help out my bf's parents in losing some weight they only slightly overweight and I know how to help his mom, but his dad is what I would call skinny fat. Now, my interpretation of skinny fat is when you more or less in your ideal BMI/weight range, but you store most of your fat in one area (usually tummy).

His Dad is skinny everywhere really except the tummy area, now yes some people have a slight tummy, but his tummy is quite round (think beer belly gut). The question I have in cases like this where it really is just one area that's big is it best to eat at a deficit or workout?

They not so into a set gym style workout, they prefer walking and possibly jogging. So, yes just checking with some people in the know if what I have been telling him is correct. That with belly fat diet plays a huge role in losing it and that I can't guarantee he will lose weight in the tummy, but since I can't really see where else the weight can come off from that he will most likely lose weight there. That his love for grapetiser is adding to the belly in the sense they both can be quiet good at eating healthy, they can cut out sweets etc, but his Dad is quite fond of the "tisers" so yes is it still okay for him to have grapetiser etc if he stays within his calories?

I know the added sugar is not good for you, but yes just checking if there is anything more I can tell him to help him lose the belly.

PS: edited to add that I used the term skinny fat since I've seen it on here before and figured people would know what I'm on about.