fog Attire if No Bridal Party??

No matter how many people you've seen post a dress code, by etiquette guests are considered adults capable of dressing themselves for a wedding. The exception is when there's an actual venue requirement. An affair can be designated as black tie as an indication of the formality of the event, but that's obviously not the case here. It's actually not proper for anyone, including bridal party and the groom to wear formal attire on the beach or anytime before 6 pm for that matter, as common as that has become to see. The relative importance of the individual is not what informs attire, it's the formality of the occasion.

he groom's father is likewise considered responsible for dressing himself. He shouldn't be asked to match the groom or told what to wear.

Formal means tux or suit actually. It also means long/fancier dresses. Are you sure this is what you want for a beach event?

In any case, you really only get to dictate what the wedding party wears.