My family and I (husband, me, and kid) have just gone there, and we stayed with my husband's cousin. We were only there for the weekend (Friday to Monday morning) and we got 200 Euros. It wasn't definitely enough. We only withdrew that much for places we did not feel comfortable paying in card or for those places where we'd only pay a small amount (avoiding too many fees).
If your cousin and friends are planning to drive, just like what we did, there is a LOT of toll fees to pay! You might want to share with that. Our cousin though just paid with card every single time, and she didn't really want us to use our card (nor pay for any of them) because of the many transaction fees we might acquire. We only paid once because the card she was using to pay for the toll was still in her purse, so I quickly handed her my card. It was around 3-4 Euros.
You might want to share with buying breakfast from the bakery. I'm not sure how much they are, but you might want to budget for that.
For souvenirs, the peddlers at the Eiffel Tower sell 5 key chains for 1 Euro, which is definitely VERY cheap. But of course, it didn't look as great as you might expect it to be, but it's good enough. For example, my kid just wants to give them to her close friends.
Use the toilets at every establishment before leaving because you have to pay for some public toilets. Also, be careful with cafes around tourist attractions. You have to make sure you get a menu to check the prices rather than relying on the server offering you drinks or specials that would be worth 15 to 30 Euros after!
Hope this helps and enjoy!