4 days into a fast and a BP of 150/110 is probably not a major issue. In the early days of a fast, with an underlying condition of raised BP,the fasting BP will often rise before going down somewhere around days 10-14. BP needs to be monitored on a consistent basis: for example immediately upon waking each morning. As a "temporary" figure 150/110 is of low concern not something to be "very worried" about. Fasting is the best way to reduce BP: be patient it will work.
I hear what you are saying about BP meds: leave that alone. Ideally, subject to good fasting preparations BP meds can in some circumstances be reduced/stopped before a fast. In your circumstances I would "leave well enough alone". As soon as you start seeing any BP decrease reduce the medication consider starting to tailor about day 6-8 in anticipation. I wouldn't worry about the fat absorption granted where you are. The probable side effect of low absorption may be to your advantage. Yes this is tricky but not of major concern with BP at 150/110. What father's subsequent readings?
Congrats for your work, interest and big support from here to the efforts your father is exerting. Well done. As you are saying in your post, food is a big issue. Weight and underlying inflamation causing many of the issues you
Just to recap quickly: although fasting is often used as a weight loss solution water only fasting is not the best advice for weight loss. A better solution is correct nutrition. Good fasting preparations are supportive and help produce excellent outcomes for fasting. Most importantly of all the post fast food regimes determine the real result. From the start of re-feeding food will be far more important than the current fast. As a side light on your father low quality nutrition can in some circumstances make fasting very difficult. An underfed body may be micro-nutrient deprived. Fasting will not help/cure that issue immediately but fasting will enhance post fast nutrient absorption.
Perhaps I should say that my first fast was for BP control.
A process I repeated a number of times for various reasons.
I have helped in fasts of a number of friends. I have no medical qualifications.