We'll go on the assumption that we are all adults and have a genuine desire to have closure on the unpleasant issues that created the family rift in the first place and wish to move forward with a positive and supportive relation(s) for the rest of our lives.
There are a few steps and even though it seems like a simple procedure, the feelings involved can make it difficult to take the necessary steps to heal and re-built relationships. More so, the people involved and the nature of the fractured bonds will complicate things even more, for instance, is the relationship between parent and child? Siblings? In-laws!
*1. Relationships between parent and children need to start with a leveled playing field, we are no longer dependent on them for survival and have achieved the status of adults, we need to behave like reasonable adults even when they treat us as if we were still five-year-olds.
*2. If the relationship is among siblings, the rift probably happened during times of immaturity and is based on rivalry and jealousy.
*3. If the issue is with the in-laws, chances are that they are set on their ways and they treat you as the guilty party in destroying their family connection or stranglehold on their "child". They resent that their kid is an adult and chooses you to be the priority in his/her life rather than them.
Communication: Start openly and state clearly that you wish to air out all disagreements and put them behind you. The goal here is to get rid of the baggage without assigning blame and move forward in a positive direction that allows all involved to have a relationship worth having and maintaining.
Forgiveness: Forgive each other for real or imaginary betrayals. Make the effort to show that you are willing to take that step and everyone is committed to not repeat the past.
Love: If you feel it, share it. Nothing gives love back like giving it first.
Respect: Clearly state the boundaries that are not to be crossed. It can be constant criticism that keeps you apart, make it clear that your actions and lifestyle are yours and so are the consequences. If you choose to have one child or twenty it is up to you and all you expect from them is love and support while you are willing to do the same for them.
Reassurance: Make it clear that you are in this for the long haul and will not disappear into the sunset with their precious child, that families can increase in size or decrease based on exclusivity. Put the ball in their court with the simple statement of "I am willing to make the effort but you have to meet me half way or this is not going to work."
Consistency: Resist the attempt of falling back into previous roles and make corrections as needed, not only in your own behavior and interactions, but whenever you see them slipping into old habits. Sometimes a gentle reminder is sufficient.
Rome was not built in a day and neither is the current state of our relationships; it took time to morph into what it is now, and it will take some time to get it back on the track we wanted to be. The good news is that it is faster to get it back on track when there is awareness of how things deteriorated and willingness to stop the erosion and rebuild a healthier relationship.