Hello,
Here is informations which you want to know.
No 1: VN catalogue: 10 (Republic of South Vietnam). 80th Birth anniv. of President Ho Chi Minh. issue: 19 May 1970.
(President Ho Chi Minh watering star-apple tree) Designer: Trần Huy Khánh
http://vietstamp.net/Product/1334/
No 2: VN catalogue: 226. The war effort. issue: Dec. 15th 1968
(US aircraft downed, after the caricature by Mai Van Hien)
http://vietstamp.net/Product/1815/
No 3: VN catalogue: 13 (Republic of South Vietnam). 2nd Anniv. of founding the Provisional Revolutionary Government of the Republic of South Vietnam. issue: 06 June 1971. Designer: Hồ Thọ
http://vietstamp.net/Product/1337/
Best regards from VSC.