Here is an example - in our family (my husband's side).
There's our family - stable family and our kids are their grandchildren. Then there's his sibling who has yet to have a non-toxic, dysfunctional relationship. Every time, they try to wrangle their way into his family's finances and get them to support their children (not his). Currently, the fiancé's children are being supported by them and I suspect they are changing their will. We expect this relationship (like all others) won't last. Then what happens? You can't change the will to not include the kids ... well, they won't feel they can. They wouldn't feel that is right.
I'm not saying your daughter's fiancé is a jerk .... ahem.. (although I think his comments are totally uncalled for), but I don't think his kids really are part of your financial responsibility. What you do with your money is your concern - not his. Their future is his concern, and his first wife's.
As for pictures, if it's going to be hurtful - I wouldn't be obvious or let the parents know. I think you could take some photos with you and the kids just for your own purposes. Have a friend take some in a nice setting some day you have them over.
I say this, because I have a friend who didn't do this, and when the second marriage split up, her kids (now grown) regret not having any pics of just them (bio kids) without their step-sibs in them. They are not close now as adults. Once their parents split up - they stopped being in contact after a few years. They wished they had more photos of their childhood and family just on their own.
We had family photos taken as one big group (different settings but all one group) and one couple split up. I had suggested we break off into families, or without spouses, etc. and the head person wasn't interested. Well, that photo isn't useable now because it's upsetting to the person who was dumped. Out of respect, no one uses it. We get a family photo once every 5-10 years when the family is all home.
I am ok with photos with different groups. I don't think it has to be obvious or hurtful. You don't have to say that things might not work out or that you just want the bio grandkids. Just have an opportunity to be in a lovely setting where you're together even with your daughter - and have someone take one. Plenty of people do that anyways.
ETA - My friends who have blended families, always take one or two with their 'bio' kids. I'm just thinking now of Facebook. They usually post the whole slew of them - and there's always a couple with just the parent and their children. It's usually less 'formal' - hugging tight or something. I've not seen it done with grandparents .. but there must be a way to do this. Maybe it would be more obvious, as the other set (step kids) wouldn't have other set of grandparents there to go off and do their pics with.
So perhaps do as I suggest, and take on another day - and do casually (so not super formal) to make less apparent.