>when 2 different [send A]'s go to the same [receive A] will there be used a "first-in first-out" procedure?yes, always.
(unless you deliberately use something such as a [pipe] or [delay] object in between, of course)
>[send]/[receive]'s inside a subpatch are they handled before [send]/[receive]'s which 'cross the border' of the subpatch?
no. the subpatch will not have any impact on the order of execution.
In general, it is bad practice to use a single send going to multiple receives - the order in which they are received should be considered undefined. You should avoid doing that if at all possible.
But in some cases, it is useful, such as sending the global BPM to different parts of your patch. In that case, you just have to be very careful that the patch doesn't depend on the order in which the different receives are triggered.