The not-cheap, but not too much joinery work would be surface espagnolette = bolts - 1 per door providing top and bottom bolts from a central handle, an= d a degree of stiffening.
I bought some nice ones from Barry Brothers, Praed St London that take euro=
-cylinder lock barrels (though didn't subsequently use them).
The much-more-work solution is to use the locks intended for pvc doors. Thi= s requires quite a bit of complicated router-work. There are specific types= intended for double doors that provide both top and bottom bolts on each d= oor into the frame, and hooks/slides from the master door into the slave.
(this type might be difficult to fit on double doors that meet in stepped o= verlap)
The latter was the solution I actually used on my doors, and I think worth = the work where appearance is important.