How many family members involved in wedding planning is...too many? Listen, I've worked with 5 different family members and it's been fine; I've also had to deal with just 1 maid of honor who almost ruined everything. It's all HOW you do it, not WHO does it. For example, I am happy to work with parents, but I don't sign contracts with them - just the couple. That draws a line, as if to say, "You may be paying for it, but it's the bride and groom's wedding!"
Here are a few wedding planning - slash - family therapy (???) tips for success.
If there's already drama, don't Collaborate.
If you already have a history with family that want to be involved - and it's not GOOD history - back away. Get a second job, elope, do whatever you can to pay for the wedding yourself and keep them from hosting. When a family member hosts, they can sometimes unfairly leverage that to control the event to the -inth degree. There was one wedding in particular that I planned, where the parents of one of the couple hosted, and whenever I spoke with them it was as if the bride and groom weren't even involved. The mom dictated the wedding colors, I had to remind them to invite the bride and groom to a table mockup - it was bizarre. On top of that, I had multiple people deciding on different things in several different emails - not an orderly 'decide by committee' way. If a family member wants to get involved and is hosting, make sure they know it's not THEIR wedding!
Divide and conquer.
"Sis, you work on the ceremony music and flowers. Mom, negotiate the venue and oversee rentals. We'll choose the officiant and DJ. Communicate directly with the planner or vendor and don't loop in all of us on every single email." That's called delegating - and it works! Back-channel chats about taste and style among all parties works for decision making, then the person in charge of that one element emails the vendor or planner directly with the final call. Done!
Tell your peeps: It's not a contest.
It makes me groan when I meet a friend or relative who tries to out-plan the planner. They're not a wedding planner, but they've done some parties and are really creative, and they go on Pinterest all the time, and now they try to take over at a walk-through or design meeting with a bride and groom. A good wedding planner has no ego and loves input, but not when it's bossy and it's a non-pro trying to throw their weight around. I had one maid of honor take over at a flower mock up and try to tell me and the florist she could "get that mercury vase at Michaels." We were like, "Yes, and we can get it and a dozen others like them at wholesale cost through our suppliers." I don't know why some people get threatened by wedding professionals - it's really weird, but it's like trying to take over negotiations on a house purchase from a Realtor. Why go through all the trouble? Let the pros do their job!