Is it appropriate for me to ask my two less active Melchizedek Priesthood holding sons to stand in the circle while my active son-in-law and another active elder anoint and bless me prior to eye surgery?
You can ask any priesthood holder you desire for a blessing. So yes it is appropriate.
However, while you do not explicitly say so, it seems from your message you are concerned about the worthiness of your two less active sons. This is understandable but we need to always remember the following.
There are three people responsible for a priesthood holder’s worthiness. The priesthood holder himself, the Bishop or other church leader in stewardship over him, and the Lord himself. As you can see you are not in this list so it is not your call.
From the Handbook of Instructions 20.1.2, Worthiness to Participate in an Ordinance or Blessing:
As guided by the Spirit and the instructions in the next paragraph, bishops and stake presidents have discretion to allow priesthood holders who are not fully temple worthy to perform or participate in some ordinances and blessings. However, presiding officers should not allow such participation if a priesthood holder has unresolved serious sins.
A bishop may allow a father who holds the Melchizedek Priesthood to name and bless his children even if the father is not fully temple worthy. Likewise, a bishop may allow a father who is a priest or Melchizedek Priesthood holder to baptize his children or to ordain his sons to offices in the Aaronic Priesthood. A Melchizedek Priesthood holder in similar circumstances may be allowed to stand in the circle for the confirmation of his children, for the conferral of the Melchizedek Priesthood on his sons, or for the setting apart of his wife or children. However, he may not act as voice.
Now if you were to ask, any priesthood holder could respond in two ways. He could decline. He might do this for many reason. It is his call to judge his own worthiness and we can and should respect that. He could also accept. Again his worthiness is between him and the Lord.
Always remember that the Lord is willing to work with and bless sinners. If He was not, none of us would have any chance at all. So do not worry about the power or effectiveness of the blessing you would get based on what you might think of the status of those giving the blessing. Rather allow the Lord to work through flawed vessels, like He always does, to bless, teach, inspire, and maybe even recover those turned away.