1)
What is the connection between "S'vam" here and "Sivmah", in Pasuk 38?
1.
Rashi (on Pasuk 38): S'vam and Sivmah are one and the same.
2)
Why did Gad and Reuven find it necessary to mention each of the towns by name?
1.
Seforno: Because each town independently was ideal for grazing livestock.