Does petition to partition force other owner to sell?

Yes, you are correct. A petition to partition is sort of like a divorce proceeding in the sense that the court must make an equitable determination of the rights of the parties who own the property.  Depending on the situation, the court may look at factors such as the respective contributions to the purchase of the property, payments made on any loan, time spent working on the property, and any other factors that may indicate one party is entitled to more or less than an even division.  The process can take months or years depending on the individual case, the issues to be resolved, and the county where the property is located.  Every county has varying back-logs of cases and different waiting periods before the parties can schedule matters before the judge.

Assuming your two siblings are able to obtain a mortgage, then they may have the option of buying your interest in the property.  If they cannot afford to buy your interest then, yes, they will have to move.  I cannot offer a good guess regarding the cost.  In addition to filing ($255) and service fees, you will have to pay for the court appointed commissioner, a broker and an appraisal fee.  Those costs will vary from case to case. I would try to work the matter out with your siblings.  If that does not work and you can afford to talk to an experienced Massachusetts real estate lawyer, he or she may be able to save you a lot of trouble and money by negotiating a settlement that satisfies the needs of all parties involved. Frequently, the other owners of a property will become more willing to discuss settlement after your attorney actually files and serves the petition.  Good luck.