My kids are nearly the same age as yours (DS2 is 12). It is tricky, as 8 & 14 yos don’t always enjoy the same things. Mine are all boys, but I guess it’s harder again maybe if you’ve got a mix (or maybe not? Genuinely don’t know)
Things we’ve done recently are; Cinema - older two watch something, 8yo & I see something else. We had friends to stay this weekend with similar aged children. I hosted a sleepover for the 12yo & some friends. We had an hour at the local trampoline park. We have a trampoline in the garden which they all use. They like toasting marshmallows on the chimnea. Swimming at the local pool. In the summer we are lucky enough to have a beach hut & everyone enjoys that (well, they did last year!) I still take the 8yo to library/Park but I leave the older two at home if they don’t want to come. My 14yo has a girlfriend, so is often out with her & friends.
My 12yo still enjoys Pokemon Go. They have started to do community days where a certain Pokemon will spawn more often & we usually do these together. The 8yo will come & do that too. 12yo & I are doing C25K together.
At weekends, the older two have sport & music lessons, DS3s tend to be in the week still, so we take a divide & conquer approach. We also do that sometimes with days out, so when the older two had an inset day recently, DH took them to London & they went on the Eye & somewhere else high (DS3 is scared of heights, so not a day he would have enjoyed)
In May half term the older two are doing 3 days on an outward bound course. Ds3 & I will probably do the zoo one day.
Hope some of this helps - it is a tricky age split.