Marrying on student Visas

Hi,

I'm trying to find out some information for a friend, she invited her brother and sister here on student visas to get them married to UK British citizens and through arranged marriage has found them both a future husband and wife to marry before their visas expire. Her brother was working full time as a student after finishing his course and we want to find out does minimum income threshold only apply to what the UK citizen earns or can it be joint income? also is it necessary to have a court marriage in this country to apply for a spouse visa or can they go back to Pakistan to marry and use the Pakistani marriage certificate from there to apply?

many thanks

Marriage is possible. Joint income may be used for a FLR(M) application.