These are modern coins from South Vietnam. The correct spelling for the smaller denomination is xu, but the French mint misspelled it as su in 1960. In 1963 the coin was restruck with the correct spelling xu.
These are low-value coins. The xu are minted in aluminum and the dong in copper-nickel. Values are less than $1 US dollar unless the coins are in pristine, fully uncirculated condition, in which case the catalog values run like this:
1960 Su: $10 fully uncirculated
1963 Xu: $5 fully uncirculated
1960 Dong: $3 fully uncirculated