It's part of a finale to a longer screenplay. I left this assault to last thinking it would be fun and easy. So far, it's neither :D
The main military action going on in France in the 14th Century was the early part of the 100 Years War (1337-1453).
In the early (14th Century) stages of this war, Castles and fortified towns provided a strong defense (even against national armies, let alone mercenaries). Strong castles and towns were usually bypassed, rather than assaulted. If it was very important to capture them, a siege, which starved out the defenders was often the only practical solution.
Edward III, for example, tried and failed to take the strong city of Calais by assault in 1346. They then settled in for a long siege, and eventually, after a year, the city surrendered, due to starvation.
Many French cities and towns, however, were not protected by strong defenses early in the 100 Years War. When Edward III attacked Caen, in 1346, the city had an old part, protected by an old wall, which had crumbled away in places, a new part, on an island, protected by three fortified bridges, and a strong castle.
When the English attacked, the French abandoned the old town, and elected to try to defend the new town on the island. The English assaulted the bridges, and also found enough boats to land archers on the island and attack the bridge defenses from the rear. The town was taken, sacked and looted. Edward tried and failed to capture the castle, and his army rode on.
Because castles and city walls were generally effective, the French and English both launched a major wave of building city defenses in the last half of the 14th century. The English built new walls around Caen. The French built new walls around Rouen starting in 1346, and Tours, in 1356. Fortifications at Reims, which had been half finished and abandoned earlier in the 14th century were rapidly completed.
Sometimes a castle or town which was besieged would agree to surrender if it were not relieved by a certain date. (The date generally being when they would run out of food). For example, the French were besieging the English held castles of Brest, La Roche sur You, and Derval, in Brittany. All three agreed terms. La Roche surrendered to the French when they were not relieved by the agreed date. Brest was relieved by an English fleet. Sir Robert Knolles managed to get through the French siege and into his castle at Derval (which had agreed to terms in his absence). When the agreed time was up for Derval, the French called on the castle to surrender. Sir Robert refused, saying that the agreement had not been made by him. The French beheaded three English hostages (two knights and a squire), Sir Robert beheaded three French knights and a squire whom he held captive in retaliation. The French withdrew, and Sir Robert continued to hold Derval.
(All according the the chronicler Froissart. https://books.google.com/books?id=cOsDAAAAQAAJ&pg=PA217&lpg=PA217&dq=siege+of+La+Roche+sur+Yon&source=bl&ots=gZv8f84q4Y&sig=vzt1UxmVIB9ALZbjhANKt8t-q-8&hl=en&sa=X&ved=0ahUKEwiDnOWh1dzJAhWPth4KHQWGCKwQ6AEIMDAE#v=onepage&q=siege%20of%20La%20Roche%20sur%20Yon&f=false)
There were only a few successful assaults on strongly fortified positions in the 14th century. In 1370, for example, the Black Prince successfully took Limoges by mining under the walls and creating a breach, allowing the attackers to take the town. There were many attempts to take strong positions by stealth or treachery. The English bribed the commander of Baupaume to surrender, but the plot was discovered by the French and when Warwick arrived, he found the commander hung from the walls in 1349. The French bribed an Italian mercenary to open a gate in Calais, but Edward III detected the plot and ambushed the French attack party.
In short, in the 14th century, the advantage was firmly with the defense, if they had a strong castle or city. National Armies could rarely take strong defenses by assault. Likewise, I suspect that mercenary bands could rarely take smaller village castles by assault.
Mercenary companies were only just emerging in the 14th century in France (they would become more prevalent in the 15th century). Mercenaries, just like national armies, would much rather raid the countryside, or unprotected towns and cities (northern France, at the start of the 100 Years War, had enjoyed about 4 generations of relative peace, so, initially, many of the town defenses were absent or neglected), than try to attack fortified positions.
The advantage of strong defenses would be greatly reduced in the 15th century, as cannon began to be deployed in the 100 Years War. In the 14th century, however, taking strongholds by assault was not a common or profitable endeavor.
Sources:
That’s the view from a broad perspective. It may be that some other contributors on this sub-reddit might know of actual examples of mercenary attacks on villages and castles from the 14th century.
If your time frame is somewhat flexible, you might want to look at castle sieges and assaults from the Albigensian Crusades in the South of France (1209-1229) in the 13th century, about 150 years earlier than the 100 Years War. That conflict had many attacks and sieges of relatively small (or at least middle sized) castles and towns. The fall of Minerve, Carcassonne, Bram, the failed assaults on Lastours, the siege of Termes, all were much smaller scale actions than those in the 100 Years War, involving smaller castles and smaller forces.
If this would work for your purposes, these sources might help:
The Song of the Cathar Wars (Chanson de la Croisade). English translation of William of Tudelle's account, written in Occitan of The Siege of Termes from The Song of the Cathar Wars: The History of the Albigensian Crusade, translated by Janet Shirley (Aldershot: Ashgate, 1996).
Historia Albigensis (The History of the Albigensian Crusade) by Pierre des Vaux-de-Cernay a contemporary chronicler in the crusader army. English translation by W.A. and M.D. Sibly (Boydell, 1998) of sections 171 to 192 of chapter 7 of the Historia Albigensis by Pierre Des Vaux-de-Cernay.