I have to agree with Robert here. If your gilt is 3 and has never bred before it's quite unlikely (not impossible, but unlikely) that she'll get 'in-pig'. Fertility decreases with age in a kind of 'use it or lose it' way
Similarly for the sow not to have been bred from in the last 3 years would make it questionable if she'll ever breed again. Sorry, I know that's not what you wanted to hear
As for keeping a single sow - it's not fair on her, especially as she gets older she may deteriorate rapidly without company (and goats, sheep and hens aren't the same as a piggy pal) If lack of time is a reason for getting rid of the two of them, surely you'll be just as tied with one ? I think in the long run it may be kinder to both of them for you to take them to slaughter. They've had a good life and deserve a good end to it, rather than being sold, transported and then ending up slaughtered anyway.
I do hope you get someone who will give them both a 'forever home' but with the price of pig food ever rising, it's getting harder to find 'pet' homes for older pigs. Good luck though and please don't think I'm trying to be negative, just realistic
Karen