HSA excess contribution situation: Need help calculating Form 8889 (complex scenario with two HSA accounts, HDHP only for part of year, and excess withdrawal already made)

Hi r/tax!  I have a complicated HSA situation and could use some guidance before I complete my 2025 tax return. I've already filed an extension so I have until October 15th, but want to get this right. I have been using Claude AI to help me and it got to a point where Claude wasn’t sure and suggested I get outside help. So I asked it to summarize what I need help with so I can post on reddit, hopefully someone can help me here.

My situation:
Filing status: Married Filing Jointly, ~$140k combined income

Previous employer (Jan 2025):
•    Had a qualifying family HDHP
•    Lost job and HDHP coverage — 1095-C shows coverage code 2C only for January, 2A for all remaining months
•    HealthEquity HSA received $500 employee + $2,050 employer contributions in January 2025
•    This matches W-2 Box 12 Code W of $2,550
•    Remaining HealthEquity balance of $4,100 was rolled over to Fidelity HSA (not a contribution)

Current employer:
•    Health plan is an Aetna HRA Medical Plan with $2,300 family deductible
•    This does NOT meet the $3,200 family HDHP minimum — so I am NOT HSA eligible with current employer

Fidelity HSA (personal):
•    Contributed $3,000 in December 2025
•    Total 2025 distributions per corrected 1099-SA: $5,708.10
•    This includes ~$4,808 in qualified medical expenses paid throughout the year
•    Already submitted excess contribution withdrawal of $900 to Fidelity before April 15th

Separate 2024 contribution:
•    $1,500 contributed in April 2025 designated as prior year (2024) contribution — not part of 2025 calculation

My questions:
1    Based on January-only HDHP coverage, my pro-rated family limit is ~$379 (1/12 × $4,550). Is that correct?
2    My total 2025 contributions are $2,550 (HealthEquity) + $3,000 (Fidelity) = $5,550. Does the $4,100 rollover from HealthEquity to Fidelity count as a contribution? I don't believe it does.
3    Am I personally responsible for the excess caused by my employer's $2,050 contribution, or does Form 8889 handle employer excess differently?
4    I already withdrew $900 from Fidelity as an excess contribution withdrawal before April 15th. The remaining excess was spent on qualified medical expenses (~$4,808). How does the spent excess get treated — income tax + 20% penalty?
5    How do I complete Form 8889 in my tax software given all of this? Specifically what goes in each relevant line?
6    Does COBRA continuation of my previous employer's HDHP count toward eligible months, and if so how do I prove/document it since my 1095-C only shows January coverage?

Documents I have:
•    1095-C showing January HDHP coverage only
•    W-2 Box 12 Code W showing $2,550
•    HealthEquity statements confirming $500 employee + $2,050 employer in January
•    Fidelity transaction history
•    Corrected 1099-SA showing $5,708.10

Any help is greatly appreciated, this has gotten more complex than I expected and I want to make sure I handle it correctly rather than get a CP2000 notice later. Thank you!