I'm assuming that the two valuations are reasonable estimates of the property value and €25K isn't a huge percentage of the property value?
And I think we should also add that the quotes should be recent.
if I was to go with lower quote to offer family which is 25k less than the other, could I do this as it is basically all I could afford reasonably as well as my own family mortgage. Would there be tax implications or would I even be allowed to offer lower price or do you have to go with most recent price?
You can offer your siblings anything you like for their shares in the property. Obviously, the lower the offer is, and the bigger the gap between wha you offer and what your siblings think (or fondly imagine) their shares are worth in today's market, the less likely they are to accept it.
If what you offer is less than the current market value, and if your siblings nevertheless do accept what you offer, then you could be looking at a gift tax liability (on top of the conveyancing and stamp duty costs that Clubman already mentioned) because your siblings would be effectively gifting you the difference between what you pay and what their shares are actually worth.
If your siblings are amenable to selling, the usual way a deal like this would proceed is that you would get an
up-to-date valuation from an estate agent agreed between you and your siblings (or a couple of valuations from a couple of agreed estate agents) and you would then offer them the value of their shares, based on that valuation (or on the average of those valuations, if more than one). That's generally seen as being fair both to you and to your siblings, and it won't give rise to any gift tax problems, because there is no element of gift in the transaction.
If you decide you can't afford to buy out your siblings on that basis, or if you are persuaded by the considerations that Clubman has mentioned that you don't want to be a landlord, then you should probably press your siblings to agree to sell the property in the open market and divvy up the proceeds. The house will deteriorate if left vacant and unused, and you'll have difficulty insuring it, etc. It's not in anybody's interests to have signficant wealth tied up in an asset that doesn't generate any income and that is progressively deteriorating.
If your siblings won't agree to this you can, in the last analysis, go to court and have the court order what is to be done with the property (which is, most likely, "sell it and divvy up the proceeds"). But that will be slow, and very expensive, and probably very destructive of your relationships with one or more of your siblings, so don't go there unless you really have no alternative.