Is William completely healthy, or does he retain his health issues from OTL but avoid his death?
In any case, a brood of English-born heirs will stabilise the succession to a significant extent- you won't get the spurious rumours that Anne wanted to leave the throne to her half-brother when she has half-a-dozen sons of her own. Given James is 27 and likely to be married with kids of his own by the time of Anne's death (OTL, at least- would having kids alter this for better or worse?) that settles things further, and with a relatively smooth transition there's no real opening for the Jacobites.
All the princes hanging about might alter courtly dynamics a fair bit- they'd have their own friends amongst the nobility, their own relationships with contentious figures like the Churchills and Abigail and Harley and such, their views and political sympathies might diverge from their mother's. Given there's five sons the likelihood of them all being in perfect harmony with their mother politically is doubtful.
Court is also likely to be livelier, IIRC OTL with Anne's ill-health things were pretty quiet and dull IOTL (cancelled celebrations and what not).
I'm not much a finance-type person, but how significant is the cost of supporting establishments for all these kids?
I'm also not much of a matchmaker, but I imagine the addition of 10 eligible English royals makes for a rather different late 17th/early 18th century marriage market.
Are there any diplomatic flow-on effects from the English royal family having strong ties to Denmark?
Anne, Mary, and Sophia would be approaching marriageable age during the William's reign. There might be tensions there if William and Anne have different views on who the best candidates are.
