Auto. join conference

Hi,
in my scenario phones from 101 to 103 call phone 100

101------------

102---------------===> 100
/
103------------/

No matter who call first (from 101 to 103) I would like that all phones auto. join conference room 1234.
Now, when first of phones established connection with phone 100 and second phone calls 100, first phone lost connection (it is on hold) and second phone has active connection.
What is wrong with my dialplan?

extensions.conf
[phones]
exten => 100,1,NoOp(Calling inosmart))
same => n,Dial(SIP/inosmart,60)
same => n,MeetMe(1234)
same => n,HangUp

exten => 101,1,NoOp(Calling android)
same => n,Dial(SIP/android,60)
same => n,HangUp

exten => 102,1,NoOp(Calling ino)
same => n,Dial(SIP/ino,60)
same => n,HangUp

exten => 103,1,NoOp(Calling and1)
same => n,Dial(SIP/and1,60)
same => n,HangUp

exten => 999,1,NoOp(Group call)
same => n,Dial(SIP/101&SIP/102&SIP/103,60)
same => n,HangUp

confbridge.conf
[default_user]
type=user
[default_bridge]
type=bridge
max_members=10
video_mode = follow_talker

meetme.conf
[general]
audiobuffers=32
[rooms]
conf => 1234