Trying to figure out my personal craziness

I hope this is the appropriate Tilde for this. If no one has any input it will still have helped me to type this out.

TL;DR In over my head with marriage, foster care, family, and work.

My wife and I became foster parents about 1.5 years ago with the intention to not adopt, but to care for children 3 and under while bio parents worked to regain custody or other permanent placements were arranged. Our first placement was two girls (7 mo and 2.5 yrs) despite wanting to do just one kid at a time (especially to start). We had them for 6 weeks and mom got them back. We had another placement (8 mo boy) for about another 6 weeks. There was a considerable lull and we were getting frustrated about not getting any new placements when the girls from our first placement were placed into custody again. So we were able to take them in again (now about 1.2 and 3.5 yrs). FF to now and we've had them for about 6 months.

We never really intended to have more than one child and for quite this long and we're struggling. My wife has always had a little less ability to weather stressful situations like this and these last 2-3 weeks I'm carrying a lot of weight. In the meantime, bio mom has gotten pregnant and there's not another hearing regarding custody for another 9 months. We fully expect that she will not be able to take them back at that time (or really realistically ever). What should probably happen would be that the county could place the kids into permanent custody (basically getting them adopted). However, from what we've heard from other foster families, temporary custody could drag on for years.

So, our main dilemma is this. We are not equipped (as a couple) to care for these kids for years. With the likely prospect of no change in custody in the near future, it feels like the best thing for these kids would be to get them into the care of someone looking to do this long-term, perhaps to eventually adopt. That being said, we absolutely love them and it feels like some kind of betrayal to force them to make yet another transition. On the other hand, with our limitations, it seems like that is inevitable anyway. Do we try to make that happen sooner?

Some other data points:
Our fostering license expires in October (about a month after the hearing is scheduled) and we don't intend to continue fostering (at least for a while, and definitely not with our current agency).
We don't have many family members close by to give us a hand with the kids, making us feel isolated and making it hard to get breaks from the kids. Our agency has not been very helpful with lining up respite care, but we're trying to be more aggressive about that now.
I've got things pretty well lined up to retire in about 5 years. My company is also just now kicking off a major project of a similar time frame and I'm in a good position to really make a mark before moving on. It will probably require some serious time commitments and effort to do it the way I want to.

Thanks for listening.