The BOAC World Air Routes map, published April 24, 1960 is linked below:
http://www.timetableimages.com/ttimages/complete/ba60/ba60-13.jpg
The facts presented in the article do NOT support their return trip by air to the USA via London, New York and San Francisco, except with some difficulty and required explanation by the author.
The facts released indicate that neither BHO Sr. nor either of Ann's parents were likely present at the birth of BHO-II at the CPGH in Mombasa.
The data showing that a COC (Certificate of Citizenship) was granted for one (1) alien during the time period, July 1, 1961 to December 31, 1961, embarking from a very large area in Africa, though not strong, DOES at least support the possibility that BHO-II was born in Kenya.
A proposed BHO-II NATIVITY TIMELINE , which I believe shows the major events occurring during the time period surrounding the birth of BHO-II in Kenya, is presented below:
Early November 1960: Ann Dunham becomes pregnant while a student at the University of Hawaii.
February 2, 1961: Ann Dunham, now about 3 months pregnant, and BHO Sr. the claimed father, allegedly are married on Maui.
Sometime in the approximate time period 2/2/1961 (marriage date) and 4/10/1961 (INS memo date): Ann and BHO Sr. attempt to make arrangements with the Salvation Army in Hawaii for the baby to be placed for adoption. ( http://www.wnd.com/2011/11/365749/ ) Apparently, the attempt to place the baby up for adoption in Hawaii was not successful.
Sometime in the approximate time period, March 1961 to April 1961: Ann, pregnant and now embarrassingly starting to show it, departs ALONE from Hawaii, via passenger cruise SHIP, and slowly heads across the ocean toward Kenya, with the intent of giving the baby to the Kenyan relatives of BHO Sr. for adoption. An extended sea voyage by Ann to Kenya, starting in the Spring of 1961, would help explain why there have not been any photos of her, while pregnant in Hawaii, publicly released.
August 4, 1961: BHO-II is born at the CPGH in Mombasa. Neither BHO Sr nor either one of Ann's parents are present at the birth. BHO Sr's relatives choose not to adopt BHO-II so Ann had no choice but to return with him to the USA. It is also possible, but less likely that Ann, feeling very maternal after the birth, decides to forget about any pre-arranged adoption with the relatives and chooses to keep her new baby son.
Mid to late August, 1961: Ann, BHO-II and possibly an American Christian Missionary who may have accompanied them, depart from Nariobi, Kenya and fly, via BOAC, first to London, and then to Vancouver, Canada.
Mid to late August, 1961: Ann and BHO-II travel the approximate 141 miles via ground transportation from Vancouver to Seattle, Washington, where Ann starts night school extension courses at the University of Washington for the Fall 1961 Semester.
At first glance, based on recent revelation of INS reports/tables I think your possible itinerary and timeline of events is very plausible.
I do believe if Obie did get a COC he somehow lost it possibly through adoption by Lolo. Since Hawaii is obviously hiding facts of his birth (maybe just the adoption, maybe birth outside the US) along with a likely chueco social security card and draft registration that he had some trouble with proving his citizenship.
Couple that with Stanley Anns missing passport records and missing National Archives records and parts of a possible puzzle fit. I still think it is possible that Madelyn Dunham accompanied Stanley Ann on her return trip, taking a week or two off work to be with the new mother and baby. It would not surprise me. It is also possible Stanley Ann left Kenya before having the baby and had it in Vancouver Canada..