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@DRD says, wood rail games hardly ever come up for sale in this country so it is very difficult to put a value on Sea Belles - it looks in lovely condition but the market of buyers is very limited.
As a pure guess I would say find the right buyer who really wants mainly to look at it and you could get £1k - £2k but most people wouldn't want to pay more than £500 to £700 for it as an "oddity" in their collection.
The Ship Mates looks nice too although desirability of the clunky multi-player games of the era is lower than the single player games (esp wedgeheads).
I would estimate you might get £500 - £800 for it.
I'd be willing to pay £400 for my own collection if it didn't sell elsewhere.
Ebay prices for games vary enormously, with often not very obvious reasons.
If you are located in the South East the chances are the bids will be higher since there are more (and more wealthy) people concentrated there
It pains me to say it but you will probably get more money for them by exporting them - if you want to go down that route try putting them on pinballowners.com as "for sale" and seeing if anyone makes an offer.
No-one there is looking for those particular titles at the moment but you never know.
You could try the Pinball Parlour in Ramsgate and see if they are interested:
https://www.facebook.com/thepinballparlour/
Also if pinball creative in London
http://www.pinballcreative.co.uk/ think they can make a turn on these games they might be able to make you a reasonable offer
Hope that helps - don't treat any of it as definitive, just my thoughts!