UNCRoss

I should have caught this, the 0.96 multiplier was removed when the WHS went into effect almost 4 years ago.  There are still some differences among different parts of the world, in Australia they calculate your Playing Handicap using a 0.93 multiplier.  
The best thing to do is to refer to the actual Handicapping Rules, which you can find here for USGA areas:
https://www.usga.org/handicapping/roh/2020-rules-of-handicapping.html
In Appendix C you'll find that the recommended formula is to take 35% of the lower handicapper and 15% of the high handicapper.  So first you calculate each players Course Handicap, then their Playing Handicap, and then use the formula to calculate the Scramble team's handicap.
No, for 9 holes you use the 35/15 formula to get an 18-hole handicap, and take half of it for a 9-hole event.  
You should check with the folks who run competitions at that course.  Most of them will require you to have an official handicap.  The handicap system relies to a large extent on peer review, with a Handicap Committee which can review posting records for each player.  They don't have the required level of access if you're using one of the private (unofficial) systems.  

Do I need an official usga handicap or are the ones on the swing u, arccos, calculator app an others sufficient?  I m joining a course next year and I didn’t know if you need an official one for tournaments or what not if I decide to do any of them.