the signs you are describing are ones we see commonly in older dogs. there are many conditions which could be causing these which i will describe below.
weight loss can be due to multiple reasons:
older animals intestines arent as good at absorbing protein which means they require a higher calorific diet to maintain the same muscle mass, for this reason you may wish to switch pablo onto a senior diet which may help with this
other reasons for weight loss can include conditions affecting the liver and kidneys which result in weight loss , this may also correlate with the signs of urinating in the house as kidney and liver issues can lead to excessive urination where animals are unable to control their bladder. urinary issues such as a urinary tract infection or prostate infection can also lead to inappropriate urination
lethargy could also be related to cardiovascular disease which would need to be assessed by your vet using a stethoscope
also, unfortunately we see cancer an internal tumours in older animals which can also lead to weight loss.
i would recommend making an appointment with your local vet for a full examination, they will be able to assess the heart and lungs to make sure there is no abnormalities here, they can feel the abdomen to check it feels normal. they may advise blood tests to assess the kidneys, liver and red and white blood cells. if they are suspecting anything concerning they may advise imaging in the form of x rays and ultrasound. i would recommend catching a urine sample in a clean plastic container which your vet will be able to test to check no sign of infection is present.
they will also be able to assess the eye and provide treatment for this is required.
i hope all this information helps