Entered on PhD, then change of mind to do 2nd Masters

See your school's DSO for switching programs, when you can switch and length of time. As long as you maintain status there is no impact on future...

Can a U.S. Permanent Resident mother apply for adjustment of status to an unmarried son over 21 years old who resides in U.S?

To adjust status the son must be in status at the time the adjustment is filed.

Change of Visa status from Tourist (B2) to an F1 student visa.

the application for change of status may not be processed timely and it may not necessarily be granted when it is decided. Consider traveling...

My Reentry permit expires in October 15, 2015 Am now in USA for 10 days , then will leave to continue my study abroad.

yes it is possible but you will need to have your biometrics completed

My Reentry permit expires in November 15, 2015 Am now in USA for 10 days , then will leave to continue my study abroad.

Yes it is possible but you will need to complete the biometrics

Yes .................................

When can parents be able to file for their children over 21 after they get their immigration through adjustment of status?

For unmarried children as soon as they are per ant residents, for married cildren after they become U.S. Citizens.

I have the L1 visa and my wife the L2, I want to divorce, will she lose her visa upon divorce?

Yes your spouse loses status as status is dependent on the relationship with the L1.

Getting work permit for f1 student visa holder

Speak with your designated school official. OPT is not likely.

Tax refund after getting green card

Not an immigration question contact a tax attorney or tax accountant.