Several points
Firstly unfair dismissal compensation certainly is capped. Compensation is based on actual financial loss, so usually just actual loss of earnings but is capped at £66k atm iirc. Unusual to get more than 6 months' pay.
Secondly, last in first out is outdated as a redundancy selection method, it's not good practice any more and could potentially be discriminatory now that age discrimination is illegal. Performance, disciplinary record, attendance record, skills and experience are much fairer selection methods, and more common, fortunately.
Thirdly, what's your DP's bosses wife doing discussing your pregnancy with your DP in the first place? How does she even know what kind of birth you are having? I would suggest he refuses to discuss it with her any further. Obviously his boss can discuss his paternity leave with him, but your DP should certainly refuse to discuss it with his wife, and should complain to his actual boss about this as well.
Fourthly, your DP certainly can't be sacked for taking paternity leave, no.
Fifthly, no he can't separate the two weeks, they must be taken together.