RD - inviting aunts and uncles?

I am close wiht my dad's 2 sisters and his brother. Each sister has a daughter who is a BM in my wedding. For the RD, should I invite my aunts and uncles (and their spouses) and the remaining cousins? I'd like to, but I don't want to overwhelm my FMIL. BTW, the RD will be a BBQ in her backyard and she is planning on having at least some of the food catered.

FH and I are going to put together a slide show of some of our baby pics and he would prefer to show it at the RD instead of the wedding bc he thinks it will break the flow of the wedding if we show it then. So if we show it at the RD, I want to have them there to see it.

What do you think? Is it okay to invite them or is that not good?

IMO- the rehersal is a special dinner just for the wedding party to thank them (and if someone in the party has a wife/husband...I'll invite them)
I just feel if you start inviting extended family, it might get out of hand.
Also, I would check with FMIL before inviting anyone else since it's her house.
And- I'd do the slideshow at the RD. I've seen it done at a wedding, and it was awkward- everything stopped.
Good luck!