As well as the idea that couples who are together for a long time start to look like each other, there is the more truthful idea that those in long-term relationships develop a similar sense of humor. These guys seem to be a prime example of the theory.
Dad has had a “brilliant” idea, and mom is helping him make it a reality. As the caption says, this is what true love looks like. Rather than rolling her eyes (although she may have done that as well), she’s right there with her partner, enjoying the lighter side of life.