First, get rid of vBSEO as soon as you can.
It is a third party product and the company that made it ceased trading years ago. The product is riddled with security holes and you WILL get compromised because of this, at some point.
DBSEO is an alternative, if you must use these type of products.
Secondly, in terms of a mobile style for vB3, I like Dartho's.
https://vborg.vbsupport.ru/showthread.php?t=263822
I still use the vB4 version of it on my site today.
You may then want to look at:
https://vborg.vbsupport.ru/showthread.php?t=226946