Thanks for your query and feel very sorry for your father for his suffering.First of all is his perineal urothrostomy opening functioning well? Does he passing urine freely through new opening?Since he has undergone valve replacement
surgery and had very bad stricture of the urethra
one has to consider about Buccal Mucosa Urrthroplsty with high risk(.In this operation structured segment of urethra is replaced by patient's own buccal mucosa )and results are satisfactory and longer lasting.As he is getting repeated attacks of urinary infection and has to take multiple Antibiotics You can think of an option of permanent Suprapubic cystostomy
.in which he will have a catheter placed in Bladder through a small hole in the bladder and the bladder will be drained continually This prevents repeated infection.and will not have to take antibiotics which themselves have side effects.