G. Marshall "Holiday" series

Short Answer: Father's Day

Only three things tie these movies together: they are set on holidays, they have intersecting rom-com storylines, and they have an embarrassment of A-list stars. 

Oh, and one more: They were all directed by Grary Marshall, a comedy legend best known for the sitcom Happy Days and its spin-offs, Laverne & Shirley and Mork & Mindy. For those of you who did not endure the '80s, that last one launched Robin Williams. 

His movies Valentine's Day, New Year's Eve, and Mother's Day are considered to form a trilogy, or at least a "trilogy."

Even though Marshall passed away in 2016, his formula could still work. So, which holiday next?

There are a billion Christmas movies, so having that holiday as the next one is out. Thanksgiving doesn't have many movies-- can you think of more than a handful?-- so it is a strong contender, even though there are umpteen TV episodes set on that day. 

Memorial Day and Veterans Day are hardly a setting for romantic comedies, and a Labor Day rom-com would be set in the world of... trade unions?

It would be hard to brand a movie Independence Day after the sci-fi blockbuster stamped that holiday as its own.

Which leaves Father's Day. Yes, there are movies about fathers aplenty, but this is a rom com, and how many of those about dads are there since... golly gee, the Courtship of Eddie's Father? 

Generally, the movies have four main plotlines that intersect so here are four for you:

1) A middle-age dad starting to date again, post-divorce, and its effect on his two kids, a 12-year-old and 15-year-old girl.

2) A granddad starting to date again, after the loss of his wife, and the effects of that on his grown sons, one who accepts it and one who cannot.

3) A couple with a teen girl who is just starting to date altogether. His mom accepts it... and her dad is freaking out.

4) A single mom trying to date again after a divorce, and having to keep in mind that she is not just looking for a husband for herself, but a dad for her kid.

The dad in 1 ends up with the mom in 4. The teen in 3 ends up getting inspired more by the granddad in 2, whom he takes cello lessons from. than his own dad; he dates the daughter in 1. 

Everything comes together at this major Father's Day picnic at the climax. There are old-fashioned games like a hoop-and-stick race, a sack race, and a "three-legged" race.