Originally from england
Can't help on hotels though, haven't been there for a while
Consider visiting the following:
Portsmouth dockyard: Mary Rose and Victory
Must go to tower of London
Hampton Court

For just nice area to visit, try Cotswolds and New Forest

I've done Weymouth a couple of times - great race! It goes through lovely countryside too, so you'll be making very efficient use of your time here to get some sightseeing done at the same time.

The main drag through Weymouth has plenty of pretty similar hotels from memory. None particularly stood out but any would do the trick and be walkable to start/finish.

Your goals and timeframe suggest to me an anti-clockwise route something like:

London: Tower, St James Palace, day trip to Hampton Court Palace, and other post-1603 attractions
Oxford
Stratford-upon-Avon: Shakespeare's birthplace, Anne Hathaway's Cottage; well preserved Tudor character
Cotwolds: pick a village to stay in for postcard England, visit Sudeley Castle
Bath
Weymouth
RACE
Relax around New Forest, recovery walks/ride
Go to Stonehenge if you must
Portsmouth (great shout from @sidelined)
Brighton, Seven Sisters (white cliffs of Dover)
RACE
London - finish any sights, optional day trip to Windsor if still unsated

Hope that helps as a starting point!

I come from Weymouth, and parents still live there. Lots of hotel that were stunning 100 years ago, but have been on a slow decline ever since. The sea front hotels have incredible sea views (make sure you get a room with sea view). I would probably recomend the Rembrandt, it's not on the sea front, however, it's really close to the IM transition, as it's not on the course, access will not be impacted

While in Weymouth visit Chesil Beach and have a walk on Portland Island (about 7 miles from Weymouth).

For the races don't forget to pack some wet weather racing options. September can be very temperamental. Having some neoprene toe covers and a Gabba type jersey would likely cover it. Consider bringing some trail shoes for the Hever run course if its wet.

To which I would add, when in Weymouth, allow time, maybe after racking bike, to roll up to Maiden Castle (small car park at road head) and marvel at this enormous iron age fort: you want heritage? That's heritage. And you'll drive past it (look hard right shortly after the turn off the A35). I cycled past it a couple of weeks ago.
https://en.wikipedia.org/...den_Castle%2C_Dorset

I live about 3 miles from Hever Castle and have done various triathlons there, so l can be of help to you

Ae you flying into Heathrow or Gatwick?

Given that you are doing Weymouth 70.3 and Hever, l would suggest you consider hiring a camper van or RV as l think you call them ! The camp site for Hever is in the field next to the event, its a big estate, very beautiful with exquisite gardens, meadows and forest. The nearest town/ railway station is Edenbridge - its a sleepy old town but the trains to London are regular and reliable. You can do your London site seeing trips this way.

I have not done Weymouth but have friends who have, so can ask them any of your questions etc.

Hever is a good course but the weather is totally unpredictable - its Britain after all. It could be anything from hot to piddling down with rain. The lake is dark water but shallow The roads for the cycle have improved massively but there are still pot holes - so l would drive the course the day before, so you spot any hazards !

Any part of the run that goes off road ie through the estate - watch for roots etc, have going flying several times there !

One of the best and really sound academic works regarding Anne Boleyn is " The Lady in The Tower " by Alison Weir, its worth reading. There is another good book about Lady Rochford who was married to Anne's brother, George. Lots of intrigue in that time and this dove tails well with Alison 's book.

There is lots to do and see, so a good plan makes sense.

Thanks! We are flying into Heathrow. My wife's favorite author is Allison Weir - she has read every one of her books so good recommendation. I'll have to get her the other book you recommended. I'm nervous about driving in London, so good idea to take train into London.

The swim at Hever Castle is my favourite ever swim. Very scenic and varied - mainly in a lake but with a section down a river - I loved it. Bad weather can really turn the site into a mud bath but the event team are used to this and manage it well with tractors on hand to help tow cars out of the parking field. My husband did the duathlon in absolutely horrible weather and was glad of trail shoes.

Definitely do not drive in London, walking and public transport are much better options.

Cannot stress this enough! I live in London (and have done all my 40+yrs) and I can tell you I've driven in Central London less than 10 times! Tube best, then rail. Buses are best avoided! (unless you want the tourist Double Decker vibe. Which I get, but the roads are too busy and they take an age to get anywhere. Uber do operate here.

Standard advice to all visitors to London. Get an "oyster" card. Its the standard pre pay touch pass you buy at all Tube and Rail stations. They'll cover you for tube, bus, rail, tram and some of the River boats.

Oyster pay as you go - Transport for London (tfl.gov.uk)

Cant believe no-one has suggested the Globe Theatre though if your wife is a fan of Tudor

Welcome to Shakespeare's Globe | London (shakespearesglobe.com)

If you're escaping London and get to Stratford (the one Upon the Avon, not the sh1thole one in East London !!) Then Macbeth is on during in Sept at the RSC in Stratford. Real culture !

Also if in the area about 70 miles from Weymouth (back towards Portsmouth - in fact the east side of the estuary to protect the route to Southampton) is Calshot castle. A Henry 8th Fort to see off any invading Spanish of French. Not a stereotypical castle of medieval times with towers and castleated battlements. But a small cannonball-proof place (one of Henry's 'Device forts'. I thought it was pretty interesting when we visited.