Broad beans belong to the legume family. They are quite hardy and will grow in most climates and soils.
They are eaten by many around the world and are grown in many gardens, allotments, and other places.
So if we can eat them, can guinea pigs eat broad beans and of they can, how much of me can be eaten.

Let’s take a look at their nutritional data, in particular their phosphorus, calcium, sugar, fat and acidic content.
% Daily Value*
Total Fat 0.7 gt1%
Saturated fat 0.1 gt0%
Polyunsaturated fat 0.3 g
Monounsaturated fat 0.1 g
Cholesterol 0 mgt0%
Sodium 25 mgt1%
Potassium 332 mgt9%
Total Carbohydrate 18 gt6%
Dietary fiber 8 gt32%
Sugar 9 g
Protein 8 gt16%
Vitamin At6%
Vitamin Ct6%
Calciumt3%
Iront8%
Vitamin Dt0%
Vitamin B-6t5%
Vitamin B-12t0%
Magnesiumt8%
source wikpedia
As you can see broad beans have a little amount of calcium, sugar and a hint of fat. They also contain a small amount of vitamin c.
This means that guinea pigs can eat broad beans but only twice to three times a week.
They are a decent legume for them to eat, that’s if they enjoy them?