I found Chiltern's Twitter team to be pretty helpful. Turns out whoever posted the timetable neglected to include the Chiltern services to/from Oxford on Easter Monday. I've got the itinerary figured out now, but it's going to be horrific. 45 minutes in Leamington Spa waiting for the train to Stratford-upon-Avon after getting in from Oxford. In Oxford, we have the choice of making a six minute connection with two tired 60+'s who aren't walking too fast after a week of touristing in London and Paris or sitting there for 30-ish minutes. It appears we'll be doing the latter, since I can't seem to find any information on which platform Chiltern will be using at Oxford. (If it was just across the platform, it'd be fine, but if we had to go up and down the stairs/lift to the other side of the tracks, that'd be too much for them in a short time.)