Hengist & Horsa were Jutish war band leaders brought in by the British King of Kent (Vortigern?), to act as mercenaries against the Saxon raiders. Thanet was allocated to them to settle in. As with most settlers, it did not take long before they looked with envious eyes at other territory in Kent and decided to take over.
Interesting that you call the incoming settlers 'English' as they were probably what we would now call Danes. I have had some interesting conversations as to what is 'Englishness'.
The term England originates from 'Angleland' i.e. the land of the Angles but these were Saxon or Germanic settlers. After the Saxons hade established themselves and taken over from the 'British' Celts, the Viking, Norse & Danish settlers come to England and in turn integrate with the Saxon population. The English shield wall on Senlac Ridge at Hastings would have been a mixture of descendants from all these earlier settlers, even King Harold was half Danish.
Post 1066 and now the Normans take over, these are Danes that had settled in Northern France and adjusted to French customs and yet by the time of Richard 1st these are also now 'English'.
History is a fascinating subject.