Complex sentence: There were reinforcements of British troops of the 35th regiment of foot from HMS "Elizabeth" which had arrived with Edward Leveson-Gower on the 29th but he declined to take part in the negotiations seeing that Hoste had everything under control.
Split into simpler sentences: There were reinforcements of British troops of the 35th regiment of foot from HMS "Elizabeth" which had arrived with Edward Leveson-Gower on the 29th. Gower declined to take part in the negotiations seeing that Hoste had everything under control.