For flights from London to Europe, check out skyscanner.net - I've used it before and it tends to do a good sweep of the cheaper airlines.
I know it's not terribly mustachian and this is a little off-the-wall given what you said you liked but I remember having a good time at zoomarine as a kid.
It's a water theme park where you can swim with dolphins, see sea lions, water slides and rapids and things.
I've just taken a look on tripadvisor and it's still got good reviews. It's less than 30 minutes from Albufeira and with little ones you could make a day of it if you did the educational shows etc.
http://www.zoomarine.pt/en/ I don't think you'll struggle avoiding gluten, it's a popular holiday destination for us Brits and as a result English is commonly spoken.
I'd thoroughly recommend the sea food over there, especially if it's been caught locally. Seabream, sardines, monkfish, squid, etc. All is incredibly good quality, it tends to be something the restaurants pride themselves on.
History isn't really my thing, but I know there's a lot of religious history and that if that were my interest I'd look to the churches first for ideas :)