Do I just say no?

[NomsQualityStreets]

I've backed myself up into a corner and I'm kicking myself for it.

DM (and DF I think) seem to think my DP is controlling or that I've "taken sides" as they've had a huge fall out and are NC. (For the record I have far from taken sides and have tried to keep a relatively middle ground).
I see them weekdays once a week for about 5-6hrs with the DCs but we generally reserve weekends for family time I.e. Me DP and DCs as due to his work he only sees them for about an hour a day through the week. DMs work days are changing and she now has EOWeekend off and wants me to come EO Saturday as its easier for DF to arrange his work too.
It's not going to work I know it isn't, if I do it then there will be tension with DP as he doesn't want to sacrifice his time as a dad with DCs in favour of DGPs (whom he doesn't get along with) and if I don't do it there will be tensions and a possible fall out between me and DM.
I know I shouldn't have but I've just been making non committal noises everytime DM had brought it up so far. Now her hours are changing next week and I feel cornered.

Part of me feels like I shouldn't care what my DM says/thinks as they've been aware weekends are generally family time but their view is "well every now and then isn't too much to ask" .
But I'm incapable of not caring and I'm also terrible at any sort of confrontation.

I personally would not mind nipping over on a Saturday for a couple of hours as it means my DBro who work through the week will be there too so I get to see him. So including driving there and back it's potentially 3-3.5 hours. (I think they might want a bit more but I wouldn't stretch any further than that to leave some family time for me and DP )
But also I feel like I should keep a United front and just say an outright 'no' as that's DPs current approach.
I've tentatively brought it up with him but he's kind of said "well tough" and that they'll just have to see DGCs every other week if that's their new schedule.

AIBU to ask for advice the best way to approach this?
WWYD?

Ps. I'm aware I'm probably coming across as a wet blanket but this is kind of the tip of the iceberg and my family situation is already bad as it is so this will be aggravating it further.

"Your parents are going to destroy your relationship"

No they're not-Op is by trying to keep accommodating the when she probably ought to just tell them to fuck off.

I'm guessing that DM is saying that DP is controlling because he's putting his foot down about jumping to her every demand. That's not controlling behaviour on his part, it's giving OP back control over herself - not something that they want to happen.

Why do you have to go every week?! That seems completely over the top to me - I see my mum about 4 times a year, granted she lives a long way away but it's fine - we talk through Facebook and messenger.

And your brother also goes every week? How did these arrangements start and are they expected of you?

I think you need to set more boundaries with your parents. 5-6 hours at a time is a lot out of yours and the children's week.

I remember the previous thread about parents being awful to you and DP and causing huge financial strain. Yes you are being hugely unreasonable staying on the fence in this case and even more unreasonable restricting DP's time with his own children to accommodate these people! You need to to back your DP on this or you are quite rightfully going to lose the relationship