Is it possible to create 7 boot partitions by editing MBR file ?
No. When using MBR you only have room for four primary entries. You can not add more.
What you can do is add an extended partition (which uses one of the three primary entries). Then you can create more partitions inside that extended partition.
Alternatively you could use GPT setup, which is highly recommended for any semi-modern hardware.
so I need 7 primary partitions.
No need for that many primary partitions. Ubuntu and feadora run fine if you use an extended partition. Same for that swap (which you only need one from which can be shared between the linux partitions.
I sspect that windows 7 & 10 like their primary partition though, or at least one shared primary /boot partition.
That leaves you with:
1) Primary boot for windows (both of them)
2) Primary win7
3) Primary win10
a) Ubuntu /
b) Ubuntu swap
c) ... (possible other Ubuntu partions sunch as /home, /usr/local, /tmp, ...)
d) Ditto other linux distributions.