Site
1. There is currently an exemption between parent and child whereby a site can be transferred to a child without incurring stamp duty or CGT where the child intends to build their home on it and it is the first such transfer. On the value of the site at 75000 you would qualify, but only if the transfer were from your mother to you in your sole name. You may need to have your husbands name on the property from a mortgage point of view to qualify on income levels.
2. If your brother transfers there is no such exemption and there is a liability to stamp duty albeit that if it is to your sole name you would halve the stamp duty payable. There may also be a charge to CGT depending on the value given when he received it from your mother. In relation to CAT, at present you can take up to 46,673 of property free from your brother but after that the balance is taxed at 20%. However as the transfer to your brother is recent, the transfer to you may be deemed a transfer from your mother for CAT purposes, in which case there is no CAT payable as the threshold is 466,725 from a parent.
3. You could have a transfer from your mother to you and then from you to your self and your spouse without incurring any stamp duty, or CGT but then there may be a charge to CAT as the revenue may deem it to be a transfer of half the value of the site from your mother to your husband, and he can only take about 23,336 from her free from CAt and after that is taxed at 20%.