Hi Chris123,
A couple of Dexters may just be o.k., they do well on scrub land - 1/4 acre could sustain a couple of pigs, but in both cases you will need to satisfy the legal and legislative requirements and you will also need to ensure the enclosures are safe and secure with good fencing (particularly for pigs) - pigs also need shelter from the sun and elements and both fields will need a supply of water...get some 'hands on' advice from a local farmer/keeper who can tell you how good the grass is - also find out if the land has been used to 'bury' anything that may cause you a problem if it is disturbed...persevere its well worth while.
Regards
Farmer