UC migration from ESA support group as a couple

My partner and I have both had M.E. for over 20 years. Initially we had separate Incapacity Benefit claims, but when we got moved to irESA we had to make one claim for the household; I am the named claimant. Since being put on irESA, I've been through 3 WCA processes, resulting in two appeal hearings and one mandatory reconsideration [all successful, the MR thanks to a complaint by my MP], but my partner hasn't been reassessed at all. I also had to complete the Work Programme, while he didn't. Basically the DWP seem to have forgotten about him, except that we receive benefit at the couple rate. A few years ago, after the second appeal, I was moved into the ESA support group and our benefit rate went up.

We're wondering what will happen specifically to my partner when we "migrate" to UC. I understand that my LCWRA status will come with me, but does my partner share that status, despite not having been involved in the WCA/ appeal process where I was put in the support group?

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A separate issue is that we had our first child a year ago, and haven't had any acknowledgement from the DWP of this change in circumstances - notified in writing but with no proof of postage etc. Shouldn't this change have triggered a "natural migration" to UC? We would be financially better off on UC as we can't make a new claim for Child Tax Credits, but we are very worried about my partner having to attend interviews etc if he doesn't have LCWRA status, or having to go through a WCA process (and likely an appeal), either of which would be exhausting and detrimental to health. If the DWP have lost/ not received/ not processed our notification of the change, is it in our interest to chase it up? Is it our responsibility to do so? (We applied for and got a Maternity Grant, so they are aware of the change somewhere in the system!) Or could we/ should we wait for "mandatory migration"?

Thanks for this.

My partner has been through the WCA previously, before we had to merge our claims (on Incapacity Benefit and on contribution-based ESA). He had also been on IB/ESA long enough to stop having to provide fit notes. He is receiving irESA now, but under my claim. So does he not bring any kind of LCW/LCWRA status with him?

The financial consideration is not the only factor for us - having been through multiple appeals before, and the work programme, we know the toll that takes on our health, and we don't know how we can deal with that and look after our baby. So putting that off may be worth the financial loss for us. That's why I'm trying to work out what situation my partner will be in when we switch.