Generally when i do a party for my DS i tailor the activities for the age that he is. The older kids can join in if they like.. I've also had the big kids be helpers with activities. They sometimes have more energy for it than the mums and dads- and also sometimes kids of that age want something to do other than chat to the grown ups.
If you do want to engage them though i wonder if you can actually just do similar activities- i would think that the big kids would even like to have a go at the paint- especially if you see if they'd like to help out the little kids. Perhaps sugest to them that they might like to add their own paints to test the colours mixing?
Do you have any lego or can you borrow any? You can have lego up on a table for them to play with, or do you have a play station or someihing you can set up?
On the bubble theme you could get the big kids to work blowing giant bubbles:
https://au.pinterest.com/pin/36239971977911222/ The little kids will love it and the big kids will get a kick out of it too...
https://au.pinterest.com/pin/170222060894363089/ you could even have a few different options for making bubbles...
Here are some other yard game ideas- the adults might like to get into a couple of them too. SOme are fairly complicated- but others seem like they could be simple and fun to set up
https://au.pinterest.com/pin/465207836484754244/That said- i wouldn't try to knock yourself out with having an activity for EVERYONE- it is a day for your LO.. so focus on making it fun for her and everyone else will have fun too!!
