Personal experience speaking.
Your father appears to have fluid accumulating in his stomach and it needs to drained. Perhaps as much a liter to four liters may be collecting in his stomach. See your doctor and and confirm. However, be sure that this will have to done on a regular basis and may require a valve to be installed on his stomach to relieve the pressure. This usually happens when there little time left 1 to 3 months .
The most promising treatments are not offered in the states. Do your research.
HIFU Canada, UK, Japan
Triology Stereostatic Radiation
Bill
High intensity focused ultrasound is not available in the US except for clinical trials. It does sound promising, though. Basically non-invasive, fewer side effects and some good results.