I am not aware of any books in English specifically looking at individual families and their military contingents in the period you are interested in. The de Bohuns are mentioned in passing in many general
books about the Domesday survey, the 12th century, the period of the Anarchy and the Baron's Wars; there is an interesting web page giving a translation from part of a French book entitled "Les Seigneurs de Bohon" here: http://mahan.wonkwang.ac.kr/link/med/so ... bohon.html
(I can not vouch for the accuracy of the translation as I have not seen the French original).
The name de Bohun is not written consistently in primary source material, as is usually the case when dealing with Anglo-Norman French. Documents mention Hunfridus de Bohum, Domesday Book 1086; Winfrisdus de Bowhun, 1120-3; William de Boun, 1119; Matildis de Bohun, reign of Henry II; John de Bown, 1275; Reginald Boon, 1279. All originally derive from Bohon in the La Manche region. These are all the same name
and all are pronounced exactly the same.
Surprisingly, Robert Bartlett's very detailed study "England under the Norman and Angevin Kings" only mentions Humphrey de Bohun very briefly as constable under Henry II (pages 55 and 257), in connection with the rebellion of 1173 -1174 and the Battle of Fornham:
". . .Royalist troops had mustered at Bury St Edmunds under the command of Richard de Lucy, the chief justiciar, Humphrey de Bohun, the constable, and the earls of Cornwall, Gloucester and Arundel. Among them were 300 knights of the king serving for wages, as well as Roger Bigod, son of the rebel earl of Norfolk. The royalists marched out under the banner of St Edmund . . ."
Clearly you can gain nothing from this about the troops of the de Bohun contingent - such details were not normally recorded in period documents at that time. All we can say is that Humphrey de Bohun was one of
the leaders of the royalist army. The Battle of Fornham (17 October 1173) has hardly been given the attention it deserves in literature and many people today have never heard of it.
Incidentally, I can guarantee that NOBODY signed Magna Carta
, despite what you might have been told. THere were more than 50 originals of that document and not one of them was signed - all carried John's Great Seal. There are today only four surviving originals and not one of them carries any signatures. The final line of text reads: Data per manum nostram in prato quod vocatur Ronimed. inter Windlesoram et Stanes, quinto decimo die junii, anno regni nostri decimo septimo.
(Given by my hand in the meadow that is called Runnymede, between Windsor and Staines, on the fifteenth day of June in the seventeenth year of our reign.)