Best is oral. Always it better with enteral feeding. If it cannot be done than other options are nasogastric feeding, peg or jejunostomy feeding etc. All of these have their limitations and specific indications.
Probably not. Total parental nutrition (TPN) is typically used when a patient has not other means of getting nutrition except through an iv. (for example their GI system is not working and can not absorb nutrients). Check with your doctor to see if there are any viable alternatives to this method of "feeding". But i suspect that if they have recommended this, they have no other good alternatives.