dont worry
1) if the compeny agree to take him on 6 months its batter he go with 6 months and start working soo he will know the compeny and his job if he want soo he can changing sponsership after 6 months.
2)his RP validity will be the same .
3)if his familly have vist RP in that case maby when its complite 5 years then it will b requid renewal from labout dept.if his familly have RP sooo in that case dont b worry.

good luck