Three weeks isn't that long; it will probably take a lot longer than that for
them to accept each other.  Even then, they may just learn to tolerate each
other rather than be loving toward each other.  That's what mine do (1 boy
and 2 older girls).  One of the females will play with the male but only when
and if she feels like it; if she doesn't and he wants to he gets hissed at.
The other just ignores him and if he gets too close she hisses and swats at
him.  This has been going on for 7 years now.  Sometimes if you can find
something they all like it helps.  I've tried giving them all catnip or
sometimes cream on one plate to get them to have to be near each other if
they want the treat but some might fight over it.  Don't worry; it'll work
out in time.  The only bad thing is if they are really hurting each other; as
long as it's just little fights once in awhile that is normal.  Sorry it's
not working out for you as quickly as you'd hoped.

Anna

Wow I really admire your dedication to what you see as a problem.
It might appear cruel to just let them sort things out but It will happen
sooner than you think.
AFAIK the text books would not suggest keeping 4 Burmese females in a small
house and the addition of 1 male Siamese (very grumpy) would seem
impossible.
It was a question of "Needs Must" and although there are still occasional
conflicts it works fine.
The conflicts consist of much growling, howling and posturing but are
usually followed by a mutual licking festival.
Give it time and don't intervene.

I think that's a great idea - get his scent out there on the furniture, etc
so the girls get used to it.  Some kitty nip might make everyone a little
more relaxed too (if they like it).  Wow the poor dude is just like mine -
has to deal with two queens in the house.  As long as he remembers he is just
the lowly male (their words, not mine) it should be okay!

Anna