How should we pay for this holiday?

[Calliemom]

Hello wise Mumsnetters, I'm looking for some advice.
We have rented a four-bed holiday cottage with a group of friends later this summer and we are very much looking forward to it. I was in charge of the booking so I told the group I would book and pay for everything and then they could pay me back. My problem is I am wondering how to divide up the total bill of 2900 pounds.
The make-up of the group is my family (two adults, two kids), a second family which is two adults and one kid, and a couple (just two adults).
All the couples will have one double bedroom each. The three children will share one bedroom (a big loft bedroom with four single beds in it).
I feel splitting the bill equally in three wouldn't be fair on the couple without children, as they are only two people and only using one bedroom. This group of friends are all in the 'very generous' category and everyone will be arguing about paying more, rather than less.
What would you do? Thank you in advance!

Id say divide into the 4 rooms. So you pay 1.5/4 asdoes other family with child. Couple pays 1/4

I would divide the price by 4 (per bedroom) so £725 per bedroom.

Couple with no children pays £725

The two couples with children each pay for one double room £725, plus half the cost of the kids room £363, so they pay £1088 each.

By bedroom:
Each couple pay 25% of the cost, parent-couples split the remaining 25% for the child bedroom.

Parent-couples stay generous with provision of wine, snacks and washing up duties in respect of childrens’ use of communal areas.

By bedroom is the fairest way.

£2900 divided by 9 people = £322 per person

So you pay £1288
Other family pay £966
Couple pay £644

By room, so each couple pays 1/4, then split 4th quarter by parents with children (either in half or 2/3 and 1/3).

100% agree with this and if people want to pay extra just tell them to buy some decent food.

Be sure to agree up front what will happen if one family drops out for whatever reason.

Split into 4 rooms so divide by 4. Couple pay 1/4 of total bill. Then divide cost of one room by 3 as 3 DC. Couple with one child pay 1/4 plus 1/3 of cost of one room. You pay 1/4 plus 2/3 of cost of fourth room.

Yes this. I think by number of bedrooms then who is using them makes sense.

Divide total cost by 9 ( per person)
Each family pay for themselves.
The couple without children shouldn't subsidise the bedroom for the children.

Everyone pays for their own room.
You pay 2/3 of the children's room and the other family pays 1/3

Great responses everyone. Thank you for your input. I am going to divide the costs by room, with a 2/3 split on the kids room (so we will pay the most). I really appreciate the advice!