Renin- it is a hormone that secreted by that kidney and it regulates the RAAS
Rennin - it is an enzyme which is secreted by stomach and helps in digestion
The 2nd one (rennin) is an enzyme present in infants which is responsible for curdling of milk n renin is an hormone secreted by the kidneys for controlling the blood pressure
renin is a hormone produced in kidney to maintain blood sodium level and rennin is an enzyme in gastric juice which helps in curdling of milk in young ones